Chapter 5 - Section 5.4 - Polynomials in Several Variables - Exercise Set - Page 376: 42

$6x^2+13xy-5y^2$

Using $(a+b)(c+d)=ab+ad+bc+bd$ or the FOIL Method, the product of the given expression, $ (3x-y)(2x+5y) ,$ is \begin{array}{l}\require{cancel} 3x(2x)+3x(5y)-y(2x)-y(5y) \\\\= 6x^2+15xy-2xy-5y^2 \\\\= 6x^2+13xy-5y^2 .\end{array}