Chapter 7 - Exponents and Exponential Functions - 7-3 Multipying Powers with the Same Base - Practice and Problem-Solving Exercises - Page 430: 41

$m^{-5}\times m^{-4}=m^{-9}$

$m^{?}\times m^{-4}=m^{-9}$ To multiply powers with the same base, we add the exponents. When we add $-4$ and the first exponent, we must get $-9$. The only way this is true is if the first exponent is $-5$ because $-5+(-4)=-9$. Therefore, $m^{-5}\times m^{-4}=m^{-9}$