A: involved in a club
B: studied 4+ hours/day
We're given that P(A) = 35.7%, P(B) = 27.8%, and P(A or B) = 53.4%. We want P(A and B).
Use the inclusion-exclusion principle:
P(A and B) = P(A) + P(B) - P(A or B)
P(A and B) = 35.7% + 27.8% - 53.4% = 10.1%