The expression can be rewritten as: $\displaystyle\frac{{\sqrt{{{3}{x}}}+\sqrt{{{12}{x}}}}}{\sqrt{{{2}}}}\cdot\frac{{\sqrt{{2}}}}{{\sqrt{{2}}}}=\frac{{\sqrt{{{6}{x}}}+\sqrt{{{24}{x}}}}}{{2}}\usepackage{cmbright}\Huge\$

Try using $\displaystyle{12}={4}\cdot{3}\usepackage{cmbright}\Huge\$ to rewrite the original expression in another way.