Incorrect. First rewrite each radical using $\displaystyle\sqrt{{{a}{b}}}=\sqrt{{a}}\cdot\sqrt{{b}}\usepackage{cmbright}\Huge\$ :

$\displaystyle{5}\sqrt{{{90}}}+\sqrt{{{40}}}+\sqrt{{{10}}}={5}\sqrt{{{9}\cdot{10}}}+\sqrt{{{4}\cdot{10}}}+\sqrt{{{10}}}={5}\cdot\sqrt{{9}}\cdot\sqrt{{{10}}}+\sqrt{{4}}\cdot\sqrt{{{10}}}+\sqrt{{{10}}}\usepackage{cmbright}\Huge\$

Simplify each term. This will give you three like terms that can be added. The correct answer is 18.