This is definately not factorable, I mean if you wanted to get technical you could use the quadratic formula and go (-b +- sqrt(b2 - 4ac))/2a:
(-6 +- sqrt((-6)^2 - 4(3)(-3)))/2(3)
= (-6 +- sqrt(36 + 36))/6
= -1 +- sqrt(72)
I think the factor would be (x - (1 -sqrt(72)))(x - (1 + sqrt(72)))
but in your case i believe you can just say its not factorable.