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: solve the quickfire maths brain teaser â ˆ š 25 % = ? 
Options: a ) 30 % , b ) 40 % , c ) 50 % , d ) 19 % , e ) 29 %
[EX A]: c

[EX Q]: Problem: alex takes a loan of $ 8,000 to buy a used truck at the rate of 9 % simple interest . calculate the annual interest to be paid for the loan amount . 
Options: a ) 680 , b ) 700 , c ) 720 , d ) 730 , e ) 750
[EX A]:
c