Using set theory, find the number of teachers who teach both Biology and Chemistry, given information about total teachers and those teaching each subject individually and in combination.

Let $C$ be the set of teachers who teach Chemistry, $B$ for Biology, and $G$ for Geography.
We are given the following information:

• Total number of teachers, $N = 150$.
• Number of teachers who teach Chemistry, $n(C) = 61$.
• Number of teachers who teach Biology, $n(B) = 65$.
• Number of teachers who teach Geography, $n(G) = 45$.
• Number of teachers who teach Biology and Chemistry but not Geography, $n(B \cap C \cap G') = 25$.

The question asks for the number of teachers who teach both Biology and