Suppose  $A_1,A_2,\mathrm{....}{A}_{30}$  are thirty sets each with five elements and $B_1,B_2,\mathrm{....}{B}_n$   are n sets each with three elements such that $\underset{i=1}{\overset{30}{\cup }}{A}_i\underset{j=1}{\overset{n}{\cup }}{B}_j=S$  . If each element of S belongs to exactly ten of the  $A_{i}s$  and exactly 9 of the $B_{j}s$  , then the value of n is ___