$2.)$ An engineer took velocity and depth readings at various points along the cross$-$section of a river, as shown below. Each velocity reading was taken between two depth readings.

a$)$ Find the total discharge of this river, expressed in cubic feet per second. Hint: Approximate the area of each portion by assuming the depth varies linearly between adjacent depth readings. Setting up a spreadsheet might be a good way to do these calculations. $(10$ points$)$

b$)$ Find the overall mean velocity at this cross$-$section of the river. $(5$ points$)$