If the function y

If the function y = .022 t² + -1.6 t + 72 represents depth y vs. clock time t, then what is the average rate of depth change between clock time t = 9.1 and clock time t = 18.2? What is the rate of depth change at the clock time halfway between t = 9.1 and t = 18.2?

What function represents the rate r of depth change at clock time t? What is the clock time halfway between t = 9.1 and t = 18.2, and what is the rate of depth change at this instant?

If the function r(t) = .176 t + -1.9 represents the rate at which depth is changing at clock time t, then how much depth change will there be between clock times t = 9.1 and t = 18.2?

What function represents the depth?
What would this function be if it was known that at clock time t = 0 the depth is 140 ?