This is how you do it!
(x-3)^2=6(x+9)
x^2 - 6x + 9 = 6x + 54
x^2 - 12x + 9 = 54
x^2 - 12x - 45 = 0
Then Factor the left side
(x + 3)(x - 15) = 0
x + 3 = 0 and x - 15 = 0
x = -3 and x = 15
The only option that can be an age is 15
Therefore the answer is 15