$\frac{2}{\sqrt{7}-\sqrt{6}}_{}-\sqrt{28}+\sqrt{54}$
$=_{}$ $\frac{2.(\sqrt{7}+\sqrt{6})}{(\sqrt{7}-\sqrt{6})(\sqrt{7}+\sqrt{6})}-2\sqrt{7}+3\sqrt{6}$
$=_{}$ $\frac{2\sqrt{7}+2\sqrt{6}}{7-6}-2\sqrt{7}+3\sqrt{6}$
$=2\sqrt{7}+2\sqrt{6}-2\sqrt{7}_{}+3\sqrt{6}$
$=5\sqrt{6}_{}$