Find the x-intercept of the parabola with vertex (6,27)and y-intercept (0,-81)

Hello,

Parabola has for equation:

y=k(x-6)²+27
and -81=k*(-6)²+27==>k=-3

so y=-3(x-6)²+27
y=-3(x²-12x+27)
if y=0==> x²-12x+27=0
Δ=12²-4*27=36=6²
==>x=9 or x=3

Where are the following equations?