Let U_{i = 1} X_{i }for i ∈ 50 = U_{i = 1} for i ∈ n Y_{i} = T, where each X_{i }contains 10 elements and each Y_{i} contains 5 elements. If each element of the set T is an element of exactly 20 of sets X_{i} 's and exactly 6 of sets Y_{i} 's, then n is equal to :

(1) 45

(2) 15

(3) 50

(4) 30