please help

Exercise 5 (4 + 4 + 4 pts). Assume you are giving 9 identical masks to 4 of your friends A, B, C, D. 1. If each friend must be given as least 1 mask, how many different assignments are there? 2. If there is no requirement (i.e., you may not give any mask to A), how many different assignments are there? 3. If A must be given at least 2 masks and B must be given as least 1 mask, how many different assignments are there? Hint: consider x1 + X2 + 23 + 24 = 9