Discovery Education
Discovery Education: Web Math: Combining Like Terms
This site explains how to simplify an expression by combining like terms. Enter an expression into the interactive "solver" and follow the step-by-step solution to learn how the answer was determined.
Wyzant
Wyzant: Combining Like Terms Worksheet
Ten multi-step linear equations are provided here from WyzAnt in an inter-active format for students to use to quiz themselves. Students enter their answers and the site grades it for them.