Homework
There are 18 class days on which homework is assigned. None of these assignments is onerous, and few of them should be more than one page in length. In fact, I think most can be adequately addressed in only about a half a page.
No individual homework assignment will receive more than 1%, thus you must submit 15 out of 18 assignments to have a chance to receive a full 15% grade for this part of the course.
Simply handing in 15 assignments is no guarantee you will receive full marks, but it is the minimum hurdle you must clear to earn them.