The number of non-negative integral solutions of $x_1+x_2+x_3+x_4=10$ is

In how many ways can a team of $3$ boys and $3$ girls be selected from $5$ boys and $4$ girls?

The number of $4$-digit numbers without repetition that can be formed using the digits $1, 2, 3, 4, 5, 6, 7$ in which each number has two odd digits and two even digits is:

In how many ways can one girl and one boy be selected from a group of $15$ boys and $8$ girls?

The value of ${}^{50}C_4 + \sum_{r=1}^{6} {}^{56-r}C_3$ is

In an election,a voter can vote for any number of candidates but not more than the number of candidates to be elected. There are $10$ candidates and $4$ are to be elected. If a voter must vote for at least one candidate,in how many ways can they vote?