Chapter 6 - Section 6.1 - The Greatest Common Factor and Factoring by Grouping - Exercise Set - Page 427: 29

$9y^4(1+3y^2)$

Factoring the $GCF= 9y^4 ,$ the given expression, $ 9y^4+27y^6 ,$ is equivalent to \begin{array}{l}\require{cancel} 9y^4 \left( \dfrac{9y^4}{9y^4}+\dfrac{27y^6}{9y^4} \right) \\\\= 9y^4(1+3y^2) .\end{array}