Hah, is that a roulette wheel for number 25? I don't think I've seen that before!

Jumping right in with the structural aspect of the challenge, you've by and large done pretty well, although there is one area where I feel it can be improved. This falls primarily to the idea of acknowledging and capturing the thickness of structures that are not, for lack of a better term, "paper-thin". There are definitely a lot of things that are going to be pretty thin in our constructions, but very rarely are things ever so thin that we can get away with only drawing the outward face of the structure without any discernible side plane to give it thickness. So for example, we can see cases like this in number 8's hubcap, the spokes on number 10, and even the outer wheel-like cylindrical structure on 23. It's also an issue with the roulette wheel in 25.

There are definitely cases where you handled this better, like number 12, although this brings me to another point I wanted to mention. For the drawings you do in this course, remember that as explained here, form shading should be left out. The way in which you use hatching and filled areas of black ink tends to lean more towards form shading, in that you're filling in those side planes, allowing the orientation of the surface to dictate whether it should be lighter or darker. In this course, we want to focus our use of filled areas of solid black for cast shadows only. These are distinct from form shading, and rely on us designing an entirely new shape that defines the relationship between the form casting it, and the surface receiving it, rather than simply filling in an existing shape.

The other thing I wanted to give a little more attention was the case in number 10, where your bike wheel's spokes were drawn with single lines. While I completely understand why you went about it in this manner, lines don't capture volume, or surface area, when used on their own. Thus, while it may force us to make them a little thicker than the original object actually required, at the very least you should draw it as a very narrow cylinder, by drawing it with two parallel edges, instead of just the single line.

Continuing onto the textural aspect of the challenge, unfortunately here you've fallen into the same trap that many have before you. In full honesty, it's an intentional trap - given how far removed we are from Lesson 2, it's very common for students to outright forget how they're meant to tackle textural problems (and unfortunately many charge forwards with whatever approach they may feel inclined to use, rather than going back and referring to Lesson 2's texture section.

How we handle texture in this course is summarized here in this short list of reminders, but it comes down primarily to the fact that we are conveying the presence of these small forms, which are arranged along the surface of a larger object (in this case the chunks that make up the tire tread), not by constructing those forms themselves, but by capturing the shadows they cast on their surroundings.

Many students default to thinking that this means they should be putting marks down haphazardly and resorting to the use of randomness to create a certain impression, but that is not what we're doing. Rather, texture as approached here is extremely time consuming. It requires us to think about the individual relationships between each textural form, and the surfaces around it, then designing a shadow shape to define that.

In your work, you had some cases like number 7 where you explicitly attempted to construct/define each individual textural form, and others like 14 where you relied more on random, arbitrary marks to give an impression, but not actually imply specific forms. In the case of 7, while this can potentially work with a wheel floating in the void as we're doing here, it becomes an issue when we try and draw a larger vehicle, as that concentration of detail and visual noise can easily result in unintentional focal points - basically drawing the viewer's eye to them whether you want them to or not. Conversely, if you look at this example of bush viper scales, you can see how working with implicit markmaking as discussed in Lesson 2, relying entirely on the shadows those forms cast, we can control how much contrast and ink is concentrated in that area, and thus avoid creating focal points where we don't want to - all while still communicating the same forms, and not changing what is actually being depicted.

Another point I wanted to call out is that in cases where the texture is made up of holes, or grooves, or even cracks, it's easy for the student to fixate on those things they can name (the holes/grooves/cracks) as being the textural form in question, and so they try and focus on how those things cast shadows. But they don't cast shadows, as they're not forms. They're an absence of form. The actual forms in question are the walls surrounding the holes, which cast shadows upon one another, and onto the floor of the hole itself. That's an important point to keep in mind, and one that is further explained in this diagram.

Now, you definitely do need to go back and review the textural principles, but that's not abnormal. It's expected at this point, and my intention with the "trap" I've laid is primarily to highlight the fact that the student's charged forwards when they should have reviewed that old material, and that perhaps their memory isn't as reliable as they might have thought. So, review that stuff (starting with these reminders from the texture section), and whatever else may have slipped your mind, and then go ahead and move onto the next (and final) lesson.