[tex]\bf 5\sqrt{28}+\sqrt{63}~~ \begin{cases} 28=2\cdot 2\cdot 7\\ \qquad 2^2\cdot 7\\ 63=3\cdot 3\cdot 7\\ \qquad 3^2\cdot 7 \end{cases}\implies 5\sqrt{2^2\cdot 7}+\sqrt{3^2\cdot 7} \\\\\\ 10\sqrt{7}+3\sqrt{7}\implies \stackrel{\textit{adding like-terms}}{13\sqrt{7}}[/tex]
