By selling 12 toffees for a dollar, a shopkeeper loses 20%

By selling 12 toffees for a dollar, a shopkeeper loses 20%. In order to gain 20% in the transaction, he should sell the toffees at the rate of how many toffees for a dollar? (a) 8 (b) 6 (c) 4 (d) 3 (e) 10