Hey guys, im really struggling with this topic. If someone could show me step by step how to do this specific question id really appreciated it.

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.