Try rearranging it into the form:
Can you take it from there?
solve the equation x^2 - (6√3)x^2 + 24 = 0 giving the answer as surds, simplified as far as possible.
i can't isolate the '6√3' without getting something wrong and ruining the equation.
You should have a look here: Practical Algebra Lessons under the "intermediate algebra topics"; it explains quadratics a lot better than I'm able to.
For the method I used (completing the square) go to Completing the Square: Solving Quadratic Equations otherwise there's also a link there on how to use the quadratic formula - which is essentially the same thing as it's derived by completing the square - where you can just plug in values into the formula to solve for