Let $\bigcup_{i=1}^{50} X_i=\bigcup_{i=1}^n Y_i=T$ 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 $X_i^{\prime} s$ and exactly 6 of sets $Y^{\prime} i s$, then $n$ is equal to
