The intensity$-$duration$-$frequency $($IDF$)$ relation for a $480$ acrewatershed is given by: $i=\frac{a{T}_r^d}{t_d^b+c}$ where $T_r$ is the return period in years, $t_d$ is the rainfall duration in minutes, $i$ is the rainfall intensity in in$/$hr$,$ and $a,b,c,$ and $d$ are empirical constants $21\mathrm{.}5,d=0\mathrm{.}23.$ The watershed is row crops and small grains on Type $B$ soil with an average runoff curve number $CN=80$ and has a time of concentration of $2$ hours. The unit peak discharge for the Type II rain for the design storm is $210csm.$

Use the NRCS peak discharge method to determine the $10-$year peak discharge for this watershed in $f\frac{t^3}{sec?}$