Chapter 7 - Exponents and Exponential Functions - 7-3 Multipying Powers with the Same Base - Practice and Problem-Solving Exercises - Page 429: 28

$\frac{-240m^{3}}{r}$

Multiply the coefficients : $-240m^{2}r^{3}r^{-4}m$ This is equivalent to : $-240m^{2}mr^{3}r^{-4}$ This becomes : $-240m^{2+1}r^{3-4}$ ,since the exponents are added while bases are the same Final result : $-240m^{3}r^{-1}$ Now $r^{-1} = \frac{1}{r}$ Hence $-240m^{3}r^{-1} = \frac{-240m^{3}}{r}$