Let \(\overset{50}{\underset{i=1}{\cup }}{X}_{i}=\overset{50}{\underset{i=1}{\cup }}{Y}_{i}=T\) where each X i contains …

Let \(\overset{50}{\underset{i=1}{\cup }}{X}_{i}=\overset{50}{\underset{i=1}{\cup }}{Y}_{i}=T\) 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