Incorrect. Use FOIL:

$\displaystyle{\left(\sqrt{{{a}}}-{2}\right)}{\left(\sqrt{{{a}}}+{4}\right)}={\left(\sqrt{{{a}}}\right)}{\left(\sqrt{{{a}}}\right)}+{\left(\sqrt{{{a}}}\right)}{\left({4}\right)}-{\left({2}\right)}{\left(\sqrt{{{a}}}\right)}-{\left({2}\right)}{\left({4}\right)}\usepackage{cmbright}\Huge\$

Simplify each term and then combine like terms. The correct answer is 2.