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: 5 drainage pipes , each draining water from a pool at the same constant rate , together can drain a certain pool in 16 days . how many additional pipes , each draining water at the same constant rate , will be needed to drain the pool in 4 days ? 
Options: a ) 6 , b ) 9 , c ) 10 , d ) 12 , e ) 15
[EX A]: e

[EX Q]: Problem: the average age of a group of 10 persons was decreased by 3 years when one person , whose age was 42 years , was replaced by a new person . find the age of the new person ? 
Options: a ) 22 , b ) 18 , c ) 12 , d ) 88 , e ) 66
[EX A]: c

[EX Q]: Problem: the product x of two prime numbers is between 17 and 60 . if one of the prime numbers is greater than 2 but less than 6 and the other is greater than 13 but less than 25 , then x = 
Options: a ) 18 , b ) 29 , c ) 37 , d ) 44 , e ) 57
[EX A]:
e