In a group of$50$ students, the number of students studying French, English, Sanskrit were found to be as follows: French$=17$, English$=13$, Sanskrit$=15$, French and English$=9$, English and Sanskrit $=4$, French and Sanskrit$=5$, English, French and Sanskrit$=3$  Find the number of students who study at least one of the three languages

In a group of$50$ students, the number of students studying French, English, Sanskrit were found to be as follows: French$=17$, English$=13$, Sanskrit$=15$, French and English$=9$, English and Sanskrit $=4$, French and Sanskrit$=5$, English, French and Sanskrit$=3$  Find the number of students who study none of the three languages

Suppose $A_1, A_2, ..., A_{30}$ are thirty sets each having $5$ elements and $B_1, B_2, ..., B_n$ are $n$ sets each with $3$ elements, let $\cup A_i$(for $i=1$ to $30$$)=\cup B_j($for $j=1$to $n)=S$ and each element of $S$ belongs to exactly $10$ of the $A_i’s$ and exactly $9$ of the $B_j’s$. then $n$ is equal to