First of all this is an equation; make it simple by dividing by -4 so that you have
x2+6x+6=0.
The only possible rational roots are 1,2,3,6 and the negatives of those choices. It is easy to rule out all of the choices.
The graph is a parabola with vertex at x=-3.
(x+3)2 = x2 + 6x + 9; therefore your original equation converts to
(x+3)2 - 3 = 0 (This is "completing the square)
and your roots are -3±√3.
The roots from the quadratic formula are [-6 ± sqrt(36-24)]/2.