A student measures a quantity $x$ five times, with the results

$5,7,9,7,8$

Calculate the mean $\stackrel{}{x}$ value.

Formula given:

$\stackrel{}{x}={\displaystyle \underset{i=1}{\overset{N}{}}}\frac{x_i}{N}$

$($a$)7\mathrm{.}2$

$($b$)7\mathrm{.}0$

$($c$)7\mathrm{.}4$

$($d$)36$