Chapter 8 - Polynomials and Factoring - 8-1 Adding and Subtracting Polynomials - Practice and Problem-Solving Exercises - Page 478: 17

$11m^3n^3$

$2m^3n^3+9m^3n^3$ These are like-terms, for the variables in both expressions are raised to the same power. Due to the fact that they are like terms, we can just add the coefficients. Therefore: $2m^3n^3+9m^3n^3=11m^3n^3$ $Tip$: When adding like terms, be sure not to change the variables or their powers.