Chapter 5 - Section 5.4 - Polynomials in Several Variables - Exercise Set - Page 375: 40

$6x^2+61xy+63y^2$

Using $(a+b)(c+d)=ab+ad+bc+bd$ or the FOIL Method, the product of the given expression, $ (x+9y)(6x+7y) ,$ is \begin{array}{l}\require{cancel} x(6x)+x(7y)+9y(6x)+9y(7y) \\\\= 6x^2+7xy+54xy+63y^2 \\\\= 6x^2+61xy+63y^2 .\end{array}