Chapter 4 - Polynomials - 4.1 Exponents and Their Properties - 4.1 Exercise Set - Page 236: 43

$\dfrac{4d^{7}}{5}$

Using $\dfrac{a^x}{a^y}=a^{x-y}$, then the expression, $ \dfrac{12d^9}{15d^2} $, simplifies to \begin{array}{l}\require{cancel} \dfrac{\cancel{3}\cdot4d^{9-2}}{\cancel{3}\cdot5} \\\\= \dfrac{4d^{7}}{5} .\end{array}