$(20$ pts$)5.$ For a $2$ hour, $10m\frac{m}{h}$ intensity rainfall, the hydrograph given in Table $4$ is observed. The area of watershed is $500k{m}^2$

Table $4.$ Propeller readings

$y$ : The last digit of your student number

b$)$ Obtain $2$ hour unit $-$ hydrograph for the considered flow section

y$=4$