A concrete lined rectangular channel with a manning's roughness

coefficient of $0\mathrm{.}015$ and

$0\mathrm{.}60$ m in width has a bed slope of $0\mathrm{.}007\frac{m}{m}.$ the channel is to carry

a discharge of $0\mathrm{.}8m\frac{3}{s}.$

a$)$ Find out the citical depth of a channel

b$)$ Find out the slope of energy grade line when the depth of the

water at a section is $0\mathrm{.}75$ m