Add. State the sum in simplest form. Then find the missing term.

$\displaystyle\frac{{{9}{a}}}{{{16}{{x}}^{{3}}}}+\frac{{{7}{a}}}{{{24}{{x}}^{{4}}}}=\frac{{{a}{\left({27}{x}+?\right)}}}{{{48}{{x}}^{{4}}}}\usepackage{cmbright}\Huge\$

The missing term is _____.