Mr. Green teaches band, choir, and math. This year, he has 57 students that take at least one of his classes. He teaches band to 25 students. There are 9 students who have Mr. Green for math and nothing else. Use the Venn diagram below: How many students take exactly 2 classes with Mr. Green?i need help with this

band alone 11 
choir alone 17 

band and choir alone 4 
band and math alone 7 
math and choir alone 6 

band choir and math 3 

math alone 9 from 11+4+10+6+17 + M = 57 
so 
2 classes = 4+7+6 = 17

17 students take exactly two classes with Mr. Green