https://openlab.citytech.cuny.edu/groups-mat-1275co-course-hub-/lessons/lesson-18-simplifying-radical-expressions-addition-and-subtraction-of-radicals/

Openstax sections:

8.2 Simplify Radical Expressions

8.4 Add, Subtract, and Multiply Radical Expressions

WeBWorK set:

SimplifyingRadicals