\[\left( 12 - \sqrt{7} \right)\left( 3 + 2\sqrt{7} \right) =\]
\[= 36 + 24\sqrt{7} - 3\sqrt{7} - 2 \cdot 7 =\]
\[= 36 + 21\sqrt{7} - 14 = 22 + 21\sqrt{7}\]