$9\mathrm{.}7$ Discharge rates for a flood hydrograph passing the point of concentration for a $600-$acte drainage basin are given in the table below. The flood was produced by a uniform rainfall rate of $2\mathrm{.}75in\frac{.}{h}r,$ which started at $9a.m.,$ abruptly ended at $11a.m.$ and resulted in $5\mathrm{.}00$ in $.$ of direct surface runoff. The base flow $($derived from influent seepage$)$ prior to$,$ during, and after the storm was $100$ cfs $.$

$\backslash$table$[[\backslash$table$[[$Time$],[$Measured$],[$discharge$]],8$ a$.$m$.,9,10,11,12,1$ p$.$m$.,2,3,4,5,6,7]]$

$($a$)$ At what times did direct runoff begin and cease?

$($b$)$ Determine the $$ index $($in$./$hr$)$ for the basin.

$($c$)$ Estimate the time of concentration $($excess release time$)$ for the basin.

$($d$)$ At what time would direct surface runoff cease if the rainfall of $2\mathrm{.}75in\frac{.}{h}r$ had begun at $9$ a$.$m$.$ and had lasted for $8$ hours rather than $2?$