2:21 AM, Wednesday August 19th 2020
Thanks for the re-upload, and congrats on finishing the challenge.
Overall you do show nice improvement through the challenge, though theres a few key principles it looks like you missed.
You have a tendency to extend your lines in the wrong direction even in your later boxes. Your parallel lines should be moving away from the viewer and towards the convergence point. In other words as explained here your extension lines will move away from the starting y when you construct your box.
Your lines get cleaner throughout the challenge which is great, however you should only be reinforcing the lines on the inside of the box, the sillouhette, none of the inner lines. Keep in mind also, if you make a mistake you must stick with it, no redrawing it or "fixing it" just let it go as trying to correct it will only draw more attention to it.
The orientation of your boxes is relatively similar here's a sheet showing some alternate orientations, try making your starting Y more varried with some lines shorter and some longer and see what happens. You can also use this generator as a starting point for a bigger variety of boxes.
Hatching lines are a great way to show orientation, make sure to keep slow and steady when you use them and be just as attentive to cleanness as any other line.
One thing that might help your overall understanding of your boxes are these notes. Thinking of your lines as parallel instead os just converging can help, in addition this construction method is often helpful in keeping mistakes form adding up.
While you've shown nice improvement theres still more I think you can get out of this challenge. Please draw 30 more boxes keeping in mind and trying to apply the stuff I've mentioned.
You've got this.