In order to buy a car, a man borrowed Rs180000 on the condition that he had to pay 7.5% interest every year. He also agreed to repay the principal in equal annual installments over 21 years. Aster a certain number of years, however, the rate of interest has been reduced to 7%. It is also known that at the end of agreed period, he will have paid in all Rs270900 in interest. For how many years does he pay at the reduced interest rate? a)7years b)12years c)14years