Moderate# Critical Numbers for Function with Rational Derivative

APCALC-OZP49G

What are the critical numbers for the function $f(x)$ that is defined for all real numbers $x$ if:

$$f^{ \prime }(x)=\cfrac { ({ x }^{ 2 }-16) }{ ({ 2x }^{ 2 }+7x-15) } $$