Chapter 4 - Polynomial and Rational Functions - 4.2 Properties of Rational Functions - 4.2 Assess Your Understanding - Page 197: 18

All real numbers except $4$ and $-3$.

The denominator of a rational function cannot be $0$. Note that when $x=-3$ or $x=4$, the denominator of the given function is equal to zero. Therefore, the domain of the given function is the set of all real numbers except $4$ and $-3$.