Chapter 7 - Exponents and Exponential Functions - 7-3 Multipying Powers with the Same Base - Practice and Problem-Solving Exercises - Page 430: 38

$5^7\times5^{-4}=5^{3}$

$5^7\times5^?=5^{3}$ To multiply powers with the same base, we add the exponents. When we add $7$ and the second exponent, we must get $3$. The only way this is true is if the second exponent is $-4$. Therefore, $5^7\times5^{-4}=5^{3}$