Chapter 5 - Section 5.4 - Polynomials in Several Variables - Exercise Set - Page 375: 12

$4x^2y+11xy+17$

Removing the grouping symbols and then combining like terms, the given expression, $ (7x^2y+5xy+13)+(-3x^2y+6xy+4) ,$ simplifies to \begin{array}{l}\require{cancel} 7x^2y+5xy+13-3x^2y+6xy+4 \\\\= (7x^2y-3x^2y)+(5xy+6xy)+(13+4) \\\\= 4x^2y+11xy+17 .\end{array}