$61m\frac{i}{h}.$ If the demand flow on the highway at the times of operation of the school zone is $90\%$ of the capacity of the highway, determine the following.

$($i$)$

$($a$)$ the velocity of the shock wave created by the operation of the school zone $($Enter the velocity of the backward forming shock wave in mi$/$h$.$ Indicate the direction with the sign of your answer.$)$

$m\frac{i}{h}$

$($b$)$ the number of vehicles affected by the school zone during this $30-$minute operation

$|$

vehicles