The figure below shows the intensity$-$duration$-$frequency $($IDF$)$ curve for Chicago, Illincin

$($a$)$ What is the return period of a storm that recorded $1\mathrm{.}0i\frac{n}{h}r$ of rainfall for $2$ hr $?$

$($b$)$ What amount of rain would have to fall in a $20-$min period to be considered a $5-yr$ storm?

$($c$)$ What is the return period of a storm that lasts $40$ min and records $4i\frac{n}{h}r$ of rainfall?

$($d$)$ A $4-$acre commercial complex in Chicago experiences a $50-$year storm event over a $1-$hr duration. During the storm event, $0\mathrm{.}2i\frac{n}{h}r$ of water evaporates, $0\mathrm{.}5i\frac{n}{h}r$ of water infiltrates, and a volume of $5$ acre$-$in accumulates on the lot. The rest leaves as runoff. Determine the total volume of runoff generated by the storm $($in acre$-$in$).$