Chapter 5 - Section 5.7 - Negative Exponents and Scientific Notation - Exercise Set - Page 409: 51

$216y^{17}$

Using the laws of exponents, the given expression, $ \dfrac{(6y^4)^3}{y^{-5}} ,$ simplifies to \begin{array}{l}\require{cancel} \dfrac{6^{1(3)}y^{4(3)}}{y^{-5}} \\\\= \dfrac{6^{3}y^{12}}{y^{-5}} \\\\= 216y^{12-(-5)} \\\\= 216y^{12+5} \\\\= 216y^{17} .\end{array}