**A battery is charged at a potential of 15 volt for 8 hours when current flowing is 10 A. The battery on discharge supplies a current of 5A for 15 hours .The mean terminal voltage during discharge is 14 volt. What is watt hour efficiency of the battery**

** (a) 50%**

** (b) 67.8%**

**(c) 89.6%**

**(d) 87.5%**