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:
Choose the correct option:
A) rs . 1800	B) rs . 1450	C) rs . 1360	D) rs . 6800	E) none

Rationale: "solution sum = s . i xt . d / ( s . i ) - ( t . d ) = 85 x 80 / 85 - 80 = rs . 1360 . answer c"
Answer: C