Suppose A_{1}, A_{2}, ..., A_{30} are thirty sets each having 5 elements and B_{1}, B_{2}, ..., B_{n }are n sets each with 3 elements, let ∪A_{i}(for i=1 to 30)=∪B_{j}(for j=1 to n)=S and each element of S belongs to exactly 10 of the A_{i}’s and exactly 9 of the B_{j}’S. then n is equal to

(A) 15

(B) 3

(C) 45

(D) 35