The drainage are of a watershed is $50 \: km^2$. The $\phi$ index is $0.5 \: cm/hour$ and the base flow at the outlet is $10 \: m^3/s$. One hour unit hydrograph (unit depth $=1 \: cm$) of the water shed is triangular in shape with a time base of $15$ hours. The peak ordinate occurs at $5$ hours.
For a storm of depth of $5.5 \: cm$ and duration of $1$ hour, the peak ordinate (in $m^3/s$) of the hydrograph is