Jumping right in with your cylinders around arbitrary minor axes, overall I'm quite pleased with your results here. You've demonstrated a good deal of care in the execution of each of your lines (using the ghosting method), in the confident execution of your ellipses (to help maintain smooth, even shapes), and ultimately in fastidiously checking the alignment of your ellipses in red. As a whole you've done a good job - I just want to warn you against one small thing.

It's something that doesn't come up too often, but with cylinders like 75 on this page, you come dangerously close to drawing the side edges such that they remain parallel on the page, rather than converging towards a far off vanishing point. While this isn't wrong, it is important to keep in mind what it represents.

When a vanishing point is at infinity (as discussed back in Lesson 1), it's not something we ourselves have direct control over. Rather, what it tells us is that the set of lines that vanishing point governs (like the side edges of the cylinder in this case) run perfectly perpendicular to the viewer's angle of sight - that they don't slant towards or away from the viewer at all. What we can do is decide that this is the case, and that we wish to draw a cylinder that aligns in such a perfect, specific manner to the viewer, and then place the vanishing point at infinity as a result.

What often happens - and again, I'm not saying that's what you're doing here (and in fact this being as rare as it is in your set suggests that it's not) is that students will feel that it's an easy way to make the cylinder challenge simpler. Avoid the convergences, and just keep everything parallel by "putting" those vanishing points at infinity, without concern for how the cylinder is actually meant to be oriented. As a rule, with these challenges (boxes, cylinders, etc.) we can pretty much trust that our forms are rotated randomly, making it very unlikely that they'd align in such a perfect manner, and thus we should always try to incorporate even the slightest bit of convergence, ensuring all our vanishing points are concrete, and non-infinite.

This really doesn't come up often in the rest of your set, but it does on occasion. For example, 95 on this page is another instance. Here in particular, with the shift in degree from one end to the other being as notable as it is, it does result in the cylinder itself feeling a little bit off. This is likely because the viewer's subconscious expects such a significant shift in degree to be matched with a similar shift in scale from one end to the other. Just another thing to keep in mind.

Moving onto your cylinders in boxes, I can definitely understand what you mean when you say "this was hard". I can definitely see that you were struggling immensely towards the beginning, and that the struggles came far less from the cylinders, and more from the boxes themselves. That, frankly, makes sense.

This exercise is really all about helping develop students' understanding of how to construct boxes which feature two opposite faces which are proportionally square, regardless of how the form is oriented in space. We do this not by memorizing every possible configuration, but rather by continuing to develop your subconscious understanding of space through repetition, and through analysis (by way of the line extensions).

Where the box challenge's line extensions helped to develop a stronger sense of how to achieve more consistent convergences in our lines, here we add three more lines for each ellipse: the minor axis, and the two contact point lines. In checking how far off these are from converging towards the box's own vanishing points, we can see how far off we were from having the ellipse represent a circle in 3D space, and in turn how far off we were from having the plane that encloses it from representing a square.

Despite that, you did push through, and I can see very clear signs of improvement throughout the set. Admittedly, based on how this part of the challenge started, I suspect you may have been a bit lax in practicing the freely rotated boxes from the box challenge as part of your regular warmup routine, so when we brought them about here once again, you floundered somewhat, and had trouble in keeping the boxes' own edges converging consistently, which only made the addition of the cylinders that much trickier.

As things warmed up and your comfort with the boxes increased, as did the rest of the challenge, and by the end I'd say that while there's still plenty of room for improvement, the core purpose of the exercise (developing your instincts towards the boxes' proportions) definitely made notable progress. So - I'll say that you should still definitely continue to practice your box challenge style boxes (along with line extensions) as part of your regular warmup routine (after all, every exercise we come across should be incorporated into that warmup routine, even those in this challenge), but that you still have completed this challenge reasonably well, and I'm pleased with the growth and improvement you've demonstrated.

So! I'll go ahead and mark this challenge as complete.