If the function y = .03 t2 + -1.2 t + 41 represents depth y vs. clock time t, then what is the average rate of depth change between clock times t = 5.1 and t = 10.2?

What function represents the rate r of depth change at clock time t?

If the rate of depth change is given by dy/dt = .204 t + -1.5 represents the rate at which depth is changing at clock time t, then how much depth change will there be between clock times t = 5.1 and t = 10.2?