The equation [tex]ax^2+bx+c=0[/tex] has it's solutions given by [tex]x= \frac{-b \pm \sqrt{b^2-4ac}}{2a}[/tex]. This is the quadratic formula.
Looking at your equation we see a=1; b=-3 and c=-6 so by the quadratic formula,
[tex]x = \frac{-(-3) \pm \sqrt{(-3)^2-(4 \times 1 \times -6)}}{2 \times 1} = \frac{3 \pm \sqrt{9+24}}{2}[/tex]
I'm sure you can work out what 9+24 is and so find the correct option :)
