Multiply the expression on the left, finding the product in simplest form. Then supply the missing number.

$\displaystyle\frac{{{{x}}^{{2}}+{5}{x}-{24}}}{{{{x}}^{{2}}-{81}}}\cdot\frac{{{x}+{9}}}{{{x}-{3}}}=\frac{{{x}+?}}{{{x}-{9}}}\usepackage{cmbright}\Huge\$

The missing number is _____.