Three parallel-plate capacitors are constructed, each having the same plate area A and with C1 having plate

Question:

Three parallel-plate capacitors are constructed, each having the same plate area A and with C1 having plate spacing d1, C2 having plate spacing d2, and C3 having plate spacing d3. Show that the total capacitance C of the three capacitors connected in series is the same as a capacitor of plate area A and with plate spacing d = d1 + d2 + d3.