A father is now three times as old as his son fiver year back he was four times as old as his son the age os son (in year) is _____?

A father is now three times as old as his son fiver year back he was four times as old as his son the age os son (in year) is _____?

Explanation

(3x-5) = 4(x-5)

3x -5 = 4x -20 

4x -3x = 20 -5

x=15