A rectangle with area A = bh is expanding with time such that the length of the base, b (t) = 1 + 2, and the height of the rectangle is constant at h = 4. What is the formula for the rate of change of the area of the rectangle with respect to time? O dA db dt dt = 21 O dA dt = (dh ) ( db ) = 0 O dA dt = h ( db ) = 81 O dt dA = b (t) = 12 + 2