In this task, you need to answer the given multiple-choice question on the general math. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

[EX Q]: Problem: what is the average of first 21 multiples of 6 ? 
Options: a ) a ) 66 , b ) b ) 77 , c ) c ) 79 , d ) d ) 81 , e ) e ) 82
[EX A]: a

[EX Q]: Problem: find out the square of a number which when doubled exceeds its one fifth by 9 ? 
Options: a ) 16 , b ) 25 , c ) 19 , d ) 26 , e ) 17
[EX A]: b

[EX Q]: Problem: in a can , there is a mixture of milk and water in the ratio 4 : 5 . if it is filled with an additional 14 litres of milk the can would be full and ratio of milk and water would become 6 : 5 . find the capacity of the can ? 
Options: a ) 40 , b ) 77 , c ) 48 , d ) 52 , e ) none of these
[EX A]:
b