A watershed is $30\%$ residential $(1/2-$acre lots$),20\%$ parks $($fair condition$),40\%$ commercial and business, and $10\%$ industrial, with corresponding soil groups of C$,$ D$,$ A$,$ and $B,$ respectively.

$($a$)$ Determine the weighted curve number for the watershed. Round to the nearest whole number.

$($b$)$ Determine the NRCS unit hydrograph. The average slope of the watershed is $2$ percent and the area is $7\mathrm{.}0m{i}^2.$ The hydraulic length is $2\mathrm{.}3mi.$