Mean Questions

Which of the following statements is true?

What is the value of x if the mean of 21, 26, 49 and x is 32?

The mean of five observations $x$, $x+2$, $x+6$, $x+4$, $x+8$ is $11$. The mean of the last three observations is:

The mean of a frequency distribution is $8.1$. If $\sum f_i{x}_i=132+5k$ and $\sum f_i=20$, then the value of $k$ is

The arithmetic mean of the six numbers $9$, $12$, $15$, $18$, $20$, and $22$ is increased by $1$ if the number $15$ is replaced by which of the following numbers?