A sum of money at simple interest amounts to Rs. 1560 in 4 years and to Rs. 1590 in 6 years. The sum is:  Choose one:
A) Rs. 1400
B) Rs. 1450
C) Rs. 1500
D) Rs. 1550
E) Rs. 1525
S.I. for 2 years = Rs. (1590 - 1560) = Rs. 30.   S.I. for 4 years = Rs.(30 x 2) = Rs. 60.   Principal = Rs. (1560 - 60) = Rs. 1500.   Answer: Option Rs. 1500
<result>C</result>
A sum of money at simple interest amounts to Rs. 1560 in 4 years and to Rs. 1590 in 6 years. The sum is: