Answer:
1) 990
2) I would have gone to the same shop and returned the extra money to the shopkeeper.
1) cost per book= Rs 78
cost of 60 books= Rs 60×78 = Rs 4680
selling price per book= Rs 78-12 = Rs 66
selling price of 60 books = Rs 66×60 =
Rs 3960
now difference = 4680-3960 = Rs 990
2) I would have returned the money to the shopkeeper as they have earned the money by using their effort and if we try to take their money away from them then their might be some problems. So we should respect their effort and return extra money if we get it.