Multiply.

$(9\sqrt[\phantom{2}]{7}-4\sqrt[\phantom{2}]{3})(\sqrt[\phantom{2}]{7}2\sqrt[\phantom{2}]{3})$

$(9\sqrt[\phantom{2}]{7}-4\sqrt[\phantom{2}]{3})(\sqrt[\phantom{2}]{7}2\sqrt[\phantom{2}]{3})=$

$($Type an exact answer, using radicals as needed. Simplify your answer.$)$