Chapter 5 - Section 5.7 - Negative Exponents and Scientific Notation - Exercise Set - Page 409: 52

$64y^{19}$

Using the laws of exponents, the given expression, $ \dfrac{(4y^5)^3}{y^{-4}} ,$ simplifies to \begin{array}{l}\require{cancel} \dfrac{4^{1(3)}y^{5(3)}}{y^{-4}} \\\\= \dfrac{4^{3}y^{15}}{y^{-4}} \\\\= 64y^{15-(-4)} \\\\= 64y^{15+4} \\\\= 64y^{19} .\end{array}