When the lights of an automobile are switched on, an ammeter in series with them reads 9.90 A and a voltmeter connected across them reads 11.80 V. When the electric starting motor is also turned on, the ammeter reading drops to 7.50 A and the lights dim somewhat. If the internal resistance of the battery is 41 m? and that of the ammeter is negligible, what is the emf of the battery?