This appears to be a conditional probability problem.
The generic formula for this is P(A\B) = P(A and B)/P(B).
Let the "A" = Student is on Math Team, and the "B" = Student is on Debate team.
So, the P(A and B) = 6/30 or 1/5. The P(A) = 15(9+6)/30 or 1/2.
You now have a complex fraction of 1/5 over 1/2. To solve this complex fraction, flip the denominator and multiply both the denominator and numerator by 2/1. This gets rid of the fraction over a fraction, and gives you a final answer of 2/5 or 40%.
