Suppose A1,A2,A3,.. , A30 are thirty sets each having 5 elements and B1,B2 ., Bn, are n sets each with 3 elements. Let ∪i=130 Ai=∪j=1n Bj=S and each elements of S belongs to exactly 10 of the Ai′s and exactly 9 of the Bj′s. Then n is equal to______