A simply supported beam has concentrated loads and cross section as shown. Determine $($a$)$ the maximum shear stress, $($b$)$ the average shear stress, and $($c$)$ the percent difference between the maximum shear stress and the average shear stress.

$[$Percent difference $[$:$=100\frac{{}_{\text{m}\text{a}\text{x}}-{}_{av}}{{}_{\text{m}\text{a}\text{x}}}$