Question

A boy is 6yrs older than his sister the product of their ages is 135'

Answer 1

x(x+6) = 135
Hmmm. 135 = 9*15, so ...

Answer 2

Sister is X yrs. old.
Boy is x+6 yrs. old.

x(x + 6) = 135.
x^2 + 6x - 135 = 0,
(x-9)(x+16) = 0,
x - 9 = 0, X = 9.
x + 16 = 0, X = -16.
Solution: X = 9. x+6 = 9+6 = 15.

Answer 3

Nine years old