A person retires at the age of 60 years. He is supposed to get from his office an annual pension of Rs. 3000 payable in half yearly installment. The office expects him to be alive for 13 more years and, therefore, it desires to set aside a fund for allowing him the pension for the period. If the sum set aside yields 8% p. a. C.1; what single sum should be set aside? ​