Question:

Use inclusion-exclusion to find the number of solutions in the non-negative integers to

\(\displaystyle X_1 + X_2 + \) .... \(\displaystyle + X_6 = 45 \) with the conditions \(\displaystyle X_j > 4\), \(\displaystyle j = 1,2,3.\)

I have no idea how to start or go about doing this problem. Any help would be much appreciated.