College Algebra (11th Edition)

$81$
Using the laws of exponents, the given expression, $\dfrac{15^4}{5^4} ,$ is equivalent to \begin{array}{l}\require{cancel} \left( \dfrac{15}{5} \right)^4 \\\\= \left( 3 \right)^4 \\\\= 81 .\end{array}