The rate of change of the volume V(t) of blood in the aorta at time t is given by V′(t) = -kP(t), where P(t) is the pressure in the aorta at time t and k is a constant that depends upon properties of the aorta. The pressure in the aorta is given by P(t) = P₀ e-mt, where P₀ is the pressure at time t = 0 and m is another constant. Letting V₀ be the volume at time t = 0, find a formula for V(t).