Since there are many things to take into account in grading this assignment, and so many different possible solution methods, I cannot give you precise grading criteria (e.g., so many points for this, so many for that). However, the following should give you some benchmarks for how the problem will be graded:
10 points: With the possible exception of at most one minor error, solution is correct, complete (including reasoning), and Writing Guidelines are followed.
6 points: Either:
a. Solution is correct and complete (including reasoning), but there are major problems with writing (e.g., the explanation is disorganized and several points are unclear); or:
b. About half of solution is provided, correct (including reasoning), and well-written, following the Writing Guidelines