suppose the brother is x years old, the man is then x+9
product of their age: x(x+9), which is =x^2 + 9x
sum of their age x+(x+9)=2x+9
(x^2+9x)/(2x+9)=20
x^2+9x=40x+180
x^2-31x-180=0
factor: (x-36)(x+5)=0
x=36 or x=-5 (this is impossible)
so the brother is 36, and the man is 45
