Ok the question reads:

A long lake is used as a reservoir to supply a hydro dam. The lake is approximately the shape of a rectangular prism with a length of 80 km, a width of 2km and a depth of 500m. On January 1st, the amound of water in the reservoir is 80 billion m^3.

The flow of water into the lake is E(t) = 90/ 2 + cos((2pi/365) t)

measured in m^3/day

The flow of water out of the lake is L(t) = 146/ 3 + cos((2pi/365) t)

measured in m^3/day

What is the rate of depth increase on the 182nd day of the year? (in cm/hour)

The answer in my text book says it's 0.4427 cm/hour

Could you please give a step by step guide, Thanks a ton

~G