The depth of water in a certain uniform cylinder is given by the depth vs. clock time function y = .026 t2 + -2.9 t + 86.  

What is the average rate at which depth changes between clock times t = 14.8 and t = 29.6?

If the rate of depth change is given by dy/dt = .144 t + -1.6 then how much depth change will there be between clock times t = 14.8 and t = 29.6?