Find the normal depth in a $15$ ft wide concrete rectangular channel $($n$=0\mathrm{.}013)$ with a slope

of $0\mathrm{.}1$ and a flow rate of $100$ cfs $.$ Also, find the average velocity. Iterate to find the answer

which is between $0\mathrm{.}1$ and $0\mathrm{.}6$ ft $.$ The error in your answer must be less than $2\mathrm{.}5\%$ calculated

using the following formula.

Error $=(()/($abs$)($f$\_($new $)-100))/(100)\backslash$times $100$