Roberts father is 4 times as old as robert. after 5 years, father will be three times as old as robert. find their present ages.

Let Robert's age is 'x'
Robert's Father's age is four times as old as Robert = 4x

In five years time, Robert's age is = x + 5
and Robert's Father's age is = 4x + 5

In five years time:
Robert's Father's age = 3 × Robert's age
4x + 5 = 3 (x+5)
4x + 5 = 3x + 15
4x - 3x = 15 - 5
x = 5

Robert's present age = 5
Robert's Father's age = 4 × 5 = 20