The mean of a set of observation is $ \overline x$. If each observation is divided by $ a, a \neq 0$ and then is increased by 10, then mean of the new set is

Question

$\begin {array} {1 1} (A)\;\large\frac{\overline x}{a} & \quad (B)\;\large\frac{\overline x+10}{a} \\ (C)\;\large\frac{\overline x+10a}{a} & \quad (D)\;a\overline x+b \end {array}$