You can put this solution on YOUR website! If this is -6/(9-3 sqrt(3))
multiply top and bottom by the conjugate, which is 9+3 sqrt (3); the conjugate product is the square of the first term minus the square of the second term, or 9^2-9*3
-6 (9+3 sqrt (3))/(81-27)
-18(3+sqrt(3))/54
-3 sqrt (3)/3