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. 75 respectively. The sum is:	Choose the correct choice from the following choices
A) 1360 B) 637.5 C) 1600 D) 1800 E) none

Rationale: "sol . sum = s . i . * t . d . / ( s . i ) - ( t . d . ) = 85 * 75 / ( 85 - 75 ) = rs . 637.5 . answer b"
Answer: B