Evaluate the following integral using trigonometric substitution.

${\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}\frac{\sqrt[\phantom{2}]{x^2-64}}{x}dx,x>8$

What substitution will be the most helpful for evaluating this integral?

A$.x=8tan$

B$.x=8sin$

C$.x=8sec$

Rewrite the given integral using this substitution.

${\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}\frac{\sqrt[\phantom{2}]{x^2-64}}{x}dx={\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}},d$

$($Type an exact answer.$)$