Question 683983
boy's age =x
father's age = y

x+y=24

(xy)/4 -x=9
multiply equation by 4
xy-4x=36
x(y-4)=36
x=36/(y-4)

Now x+y = 24
substitute x in the equation

36/(y-4) +y = 24

multiply equation by (y-4)
36+y(y-4)=24(y-4)

36+y^2-4y=24y-96

y^2-4y-24y+36+96=0

y^2-28y+132=0

y^2-22y-6y+132=0

y(y-22)-6(y-22)=0
(y-22)(y-6)=0

y=22 OR 6

Father's age = 22

Son's age = 2  (because x+y=24)