a coil takes 15 min to boil a certain amount of water  another coil takes 20 min to boil the same process. Find time taken to boil the same amount of water whn both coils are connected in series... ans given is 35 min but im getting 8.6 min...

the prob is that im using the formula H= i^2 Rt coz they are connected in series but they are using H=V^2/Rt..

plzz post the complete solution