Find the product in simplest form and supply the missing number.

$\displaystyle\frac{{{{x}}^{{2}}-{64}}}{{{{x}}^{{2}}+{7}{x}-{30}}}\cdot\frac{{{x}-{3}}}{{{x}-{8}}}=\frac{{{x}+{8}}}{{{x}+?}}\usepackage{cmbright}\Huge\$

The missing number is _____.