Y=ax^2-bx-12.find the value of x? when a=1,b=2,y=3 by using general formular

Find the value of x when a=1, b=2, y= 3 by using general formula
After replace number in a, b, y we have
3 = 1ax^2 - 2x - 12
x^2 - 2x -15 = 0
x^2 - 5x + 3x -15 = 0
(x^2 - 5x) + (3x -15) = 0
x*(x - 5) + 3*(x - 5) = 0
(x - 5)*(x + 3) = 0
x - 5 = 0 or x + 3 = 0
x=5 or x=-3

Ithink your answer is b