Fathers age is 5 times his sons age 4 years back the father was 9 times older than son Find the fathers present age?

Father's age is 5 times his son's age. 4 years back the father was 9 times older than son. Find the fathers present age. a) 45 years b) 40 years c) 50 years d) 35years

Cute , he's 40 & the kid is 8 Mathematic explanation:

x = father's age

y = son's age

x = 5y

x-4 = 9(y-4)

x-4 = 9y-36

x = 9y-32

5y = x = 9y-32

5y = 9y-32

4y = 32

y = 8

x = 5y = 40