[tex]\displaystyle\bf\\\frac{6}{2\sqrt{3} -3} =\frac{6\cdot(2\sqrt{3}+3) }{(2\sqrt{3} -3)\cdiot(2\sqrt{3}+3) } =\frac{6\cdot(2\sqrt{3}+3) }{(2\sqrt{3} )^{2}-3^{2} } =\\\\\\=\frac{6\cdot(2\sqrt{3}+3) }{12-9 } =\frac{6\cdot(2\sqrt{3}+3) }{3 }=2\cdot(2\sqrt{3} +3)[/tex]