$($b$)$ Using the $3-$hour unit hydrograph, predict the flow hydrograph likely to result from $2$ consecutive rainfall events, A and B$.$ Rainfall event B occurs $2$ hours after A$,$ and the characteristics of the rainfall events are as follows:

Rainfall event A: Intensity $12m\frac{m}{h}r$ duration $3$hours

Rainfall event B: Intensity $6m\frac{m}{h}r$ duration $2$ hours

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