In this task, you need to answer the given multiple-choice question on the gain. Gain is the value by which to multiply the input. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

[EX Q]: Problem: at what rate percent per annum will the simple interest on a sum of money be 4 / 5 of the amount in 10 years ? 
Options: a ) 4 % , b ) 7 % , c ) 8 % , d ) 3 % , e ) 1 %
[EX A]: c

[EX Q]: Problem: if a lends rs . 2000 to b at 15 % per annum and b lends the same sum to c at 17 % per annum then the gain of b in a period of 4 years is ? 
Options: a ) 155 , b ) 162 , c ) 157.5 , d ) 160 , e ) 157.12
[EX A]: d

[EX Q]: Problem: the simple interest and the true discount on a certain sum for a given time and at a given rate are rs . 90 and rs . 80 respectively . the sum is : 
Options: a ) 1360 , b ) 1450 , c ) 720 , d ) 1800 , e ) none
[EX A]:
c