$6-$ A new $7$ ha suburban development is to be serviced by a trunk storm sewer that discharges to a local stream. Use the rational method $($Q$=$ CiA$)$ to estimate the peak surface runoff in m$3[$d$.$ Assume a typical runoff coefficient $($C$)$ for a suburban development, time of concentration is $30$ minutes and the local IDF relationship is given by

i $=60\mathrm{.}3$td$,$ where td is the rainfall duration in hours and i is the intensity in mm$/$hr$.$ Clearly state any assumptions made in your answer.