Explanation:
let father's age = x
son's age = y
Five years hence, age of father = x+5
age of son =y+5
So (x+5)= 3(y+5)
⇒x=3y+10
Five years ago, age of father = x-5
age of son = y-5
Sox-5=7(y-5)
⇒3y + 10-5=7y - 35
⇒ 4y = 40
⇒y=10 <<<<<<<
x = 3y +10= 40 <<<<<