Suppose A1, A2, ... 30 are thirty sets, each with five elements and B1, B2, ...., Bn are n sets each with three elements. Let $\bigcup_{i=1}^{30} A_i= \bigcup_{j=1}^{n} Bj= S$. If each element of S belongs to exactly ten of the Ai' s and exactly nine of the Bj' s then n=