y = a(x - p)(x - q)
p and q are the zeros of the parabola, -6 and 6 y = a(x + 6)(x - 6)
Substitute third point (0, 36) into the above equation to solve for a.
y = a(x + 6)(x - 6)
36 = a(0+6)(0-6)
36 = a(-36)
a = -1
So the equation is
y = -(x + 6)(x - 6)