Chapter 5 - Section 5.4 - Polynomials in Several Variables - Exercise Set - Page 375: 11

$2x^2y+13xy+13$

Removing the grouping symbols and then combining like terms, the given expression, $ (4x^2y+8xy+11)+(-2x^2y+5xy+2) ,$ simplifies to \begin{array}{l}\require{cancel} 4x^2y+8xy+11-2x^2y+5xy+2 \\\\= (4x^2y-2x^2y)+(8xy+5xy)+(11+2) \\\\= 2x^2y+13xy+13 .\end{array}