A double decked bus can accomodate 50 passengers,20 in the upper deck…

A double decked bus can accomodate 50 passengers,20 in the upper deck and 30 in the lower deck.In how many ways can the passengers be accomodated if 15 refuse to be in the upper deck while 10 others refuse to be in the lower deck?

This problem repeats another one in the library (at most with different numbers), so it's left out of browsing.

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #3171