$\begin{array}{l}
\left( {\sqrt {75} + \sqrt {243} - \sqrt {48} } \right):\sqrt 3 \\
= \sqrt {25.3} + \sqrt {81.3} - \sqrt {16.3} \\
= \left( {\sqrt {25} .\sqrt 3 + \sqrt {81} .\sqrt 3 - \sqrt {16} .\sqrt 3 } \right):\sqrt 3 \\
= \sqrt 3 \left( {\sqrt {25} + \sqrt {81} - \sqrt {16} } \right):\sqrt 3 \\
= \sqrt {25} + \sqrt {81} - \sqrt {16} \\
= 5 + 9 - 4 = 10
\end{array}$
