Varun is three times as old as his sister. Six years hence the product of their ages will be 231. Find Varun’s present age.

Correct option is D

Given:

Varun is three times as old as his sister.

Solution:

Let age of Varun sister = x

So age of Varun = 3x

According to question

6 year hence there age product is 231

(x+6)(3x+6) =231

(x+6)(3x+6) = 11$$\times 21$$ 

​(x+6)(3x+6) = (5+6)(3$$\times$$5 +6)

So, x =5 we solve this question by11$$\times 21$$  because when we have a prime factor than it is easy to solve by direct factorization.  

Varun age $$\implies$$​3x = 15 years