Let $\underset{i=1}{\overset{50}{U}}{X}_i=\underset{i=1}{\overset{n}{U}}{Y}_i=T,$ where each $X_i$ contains 10 elements and $Y_i$ contains 5 elements. If each element of the set T is an element of exactly 20 of sets $X_i^{\text{'}}s$ and exactly 6 of sets $Y_i^{\text{'}}s,$ is then n is equal to