I've been struggling with this question:

In how many ways can you grade 5 students so their average is 60? Note that each student's grade is an integer, no greater than 100 and no lower than 0.

I know that no more than 3 students can get a 100, but I don't see a way to count all the possible permutations for dividing 300 points into 5 baskets, so each of them is no more than 100 points.

I'd be grateful if you could hint me the right direction for solving this problem.