Answer:
Let the present ages of man and son be x and y respectively
x+y = 45
5 yrs ago , age of man = (x-5)
age of son = (y-5)
(x-5)(y-5) = 4(x-5)
(y-5) = [4(x-5)] / (x-5)
y-5 = 4. [(x-5) got cancelled out]
y = 9 yrs
x+y = 45 yrs
x+9 = 45
x = 45-9 yrs => 36 yrs
