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'.

Let me give you an example: Problem: on a sum of money , the simple interest for 2 years is rs . 330 , while the compound interest is rs . 340 , the rate of interest being the same in both the cases . the rate of interest is 
Options: a ) 15 % , b ) 14.25 % , c ) 6.06 % , d ) 10.5 % , e ) 11.5 %
The answer to this example can be: c
Here is why: "explanation : the difference between compound interest and simple interest on rs . p for 2 years at r % per annum = ( r ã — si ) / ( 2 ã — 100 ) difference between the compound interest and simple interest = 340 - 330 = 10 ( r ã — si ) / ( 2 ã — 100 ) = 10 ( r ã — 330 ) / ( 2 ã — 100 ) = 10 r = 6.06 % answer : option c"

OK. solve this:
Problem: a sum of rs . 12,500 amounts to rs . 15,500 in 4 years at the rate of simple interest . what is the rate of interest ? 
Options: a ) 3 % , b ) 4 % , c ) 5 % , d ) 6 % , e ) 7 %
Answer:
d