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'.

Problem: what is 120 % of 13 / 24 of 840 ? 
Options: a ) 436 , b ) 478 , c ) 512 , d ) 546 , e ) 620
d

Problem: 40 is subtracted from 70 % of a number , the result is 30 . find the number ? 
Options: a ) 150 , b ) 997 , c ) 266 , d ) 288 , e ) 100
e

Problem: a motorcyclist x drives along a circular fence at a rate of 2 rounds per hour and another motor cyclist y at a rate of 4 rounds per hour . after how long they will cross each other for the first time ? 
Options: a ) 10 min , b ) 20 min , c ) 30 min , d ) 40 min , e ) none of these

c