You have the following expression:
[tex]-\sqrt[]{63}[/tex]In order to simplify the previous expression, consider that 63 = 7*9 = 7*3^2.
Then, you have:
[tex]-\sqrt[]{63}=-\sqrt[]{7\cdot9}=-\sqrt[]{7\cdot3^2}=-3\sqrt[]{7}[/tex]Hence, the simplified expression is
-3√7
