What is the discharge of water moved by a river that has an area of 750m and is traveling 4 m/s?

The question is simply asking for the volumetric flow rate of the water in the river. It is the volume of fluid which passes per unit time. It has units of m^3 / s. We calculate as follows:

Q = 750 m^2 (4 m/s) = 3000 m^3/s

Hope this answers the question. Have a nice day.