so just you need to rationalize the denominator so multiple top and bottom by conjugate so by sqrt6 +sqrt3
8 8(sqrt6 +sqrt3) 8(sqrt6 +sqrt3)
----------------- = ------------------------------------- = ----------------------- =
sqrt6 - sqrt3 (sqrt6 -sqrt3)(sqrt6 +sqrt3) 6 -3
8(sqrt6 +sqrt3)
= -----------------------
3
hope this will help you
