Chapter 5 - Section 5.3 - Special Products - Exercise Set - Page 368: 67

$9y^2-49$

Using $(a+b)(a-b)=a^2-b^2$ or the special product of the sum and difference of like terms, the product of the given expression, $ (3y+7)(3y-7) ,$ is \begin{array}{l}\require{cancel} 3y(3y)-7(7) \\\\= 9y^2-49 .\end{array}