A submarine is diving toward the bottom of the ocean. The depth of the submarine, D, in feet below sea level, after t minutes have elapsed is given by the function D(t) 20+16t. The pressure, P, in pounds per square inch, exerted on the submarine at a depth of z feet is given by the function P(z) 14.7+0.445r Find an explicit expression that models the pressure exerted on the submarine as a function of the elapsed time, t, in minutes.