hello,
the question presented deals with surds and basic knowledge or rules of surds would make it easy to simplify
[tex]3\sqrt{6}\text{ }-\text{ 4}\sqrt{6}[/tex]
note: both of them have identical roots i.e square root of 6 so we can easily subtract it
[tex]\begin{gathered} 3\sqrt{6}-\text{ 4}\sqrt{6} \\ \text{the roots are identical i.e }\sqrt{6} \end{gathered}[/tex]
since they're both identical, they'll have the same root
[tex]\begin{gathered} 3\sqrt{6}\text{ }-\text{ 4}\sqrt{6} \\ (3-4)\sqrt{6} \\ -1\sqrt{6}\text{ = }-\sqrt{6} \end{gathered}[/tex]
