The simple interest and the true discount on a certain sum for a given time and at a given rate are Rs. 85 and Rs. 80 respectively. The sum is:_______?

The simple interest and the true discount on a certain sum for a given time and at a given rate are Rs. 85 and Rs. 80 respectively. The sum is:_______?

A. Rs. 1800
B. Rs. 1450
C. Rs. 1360
D. Rs. 6800