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'.

[Q]: Problem: calculate how many seconds it will take for 4 bells to toll together again , given that they begin to toll together respectively at the intervals of 9 , 10 , 14 and 18 seconds . ? 
Options: a ) 636 , b ) 631 , c ) 633 , d ) 610 , e ) 630
[A]: e


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


[Q]: Problem: the income of a company increases 20 % per annum . if its income is 2664000 in the year 1999 what was its income in the year 1997 ? 
Options: a ) 2220000 , b ) 2850000 , c ) 2121000 , d ) 1855000 , e ) none of these
[A]:
e