Q$5.$ Rational Method $(15$ Points$)$

Find the design flow for a $100-$year rainfall. The area is $20$ acres; the runoff coefficient was shown in the table below. The time of concentration is $40$min

$\backslash$table$[[\backslash$table$[[$Area$],[($acre$)]],\backslash$table$[[$Runoff$],[$Coefficient$]]],[6,0\mathrm{.}46],[5,0\mathrm{.}80],[5,0\mathrm{.}52],[4,0\mathrm{.}34]]$