Assume that a rectangle with sides x and y is expanding with time. Let y = 2x and x(t) = 31 + 1. What is the formula for the rate of change of the area with respect to time? dA = 12(3-1) dt dA dt = (31 + 1) dA A = 4(31 - 1) dt dA dt == 12(31 + 1)