There are five cells combined in series to form a battery. A light bulb with a resistance of 4 ohms was attached to it and the power was 1.5A when the light bulb was replaced by an electric fan with a...

There are five cells combined in series to form a battery. A light bulb with a resistance of 4 ohms was attached to it and the power was 1.5A when the light bulb was replaced by an electric fan with a resistance of 9 ohms the power was 0.75A. Find the internal resistance of each cell.