Ravi is 12 years younger than Surya. Ravi's age is 40 % of the sum of his and Surya's age. What will be Surya's age 9 years hence? 

Let the age of Surya = x yrs Then the age of Ravi = (x - 12) yrs

 So according to question

$\begin{array}{l}(x-12)=(x+x-12)\frac{40}{100}\\ 5x-60=4x-24\\ x=36\end{array}$

So after 9 yrs Surya's age= 36 + 9 = 45 yrs