Chapter 5 - Section 5.2 - Negative Exponents and Scientific Notation - Exercise Set - Page 353: 43

$-\frac{4a^{5}}{b}$

We know that $a^{−n}=\frac{1}{a^{n}}$ and $\frac{1}{a^{-n}}=a^{n}$ (as long as a is a nonzero real number and n is an integer). Therefore, $\frac{-24a^{6}b}{6ab^{2}}=\frac{-24}{6}\times a^{6-1}\times b^{1-2}=-4\times a^{5}\times b^{-1}=-4\times a^{5}\times\frac{1}{b}=-\frac{4a^{5}}{b}$.