The expression can be rewritten as: $\displaystyle\frac{{\sqrt{{{7}{x}}}+\sqrt{{{28}{x}}}}}{\sqrt{{{2}}}}\cdot\frac{{\sqrt{{2}}}}{{\sqrt{{2}}}}=\frac{{\sqrt{{{14}{x}}}+\sqrt{{{56}{x}}}}}{{2}}\usepackage{cmbright}\Huge\$

Try using $\displaystyle{28}={4}\cdot{7}\usepackage{cmbright}\Huge\$ to rewrite the original expression in another way.