Here are the completed facts about substitution using the words you've provided:
- If two amounts are equal, you can substitute one for the other.
- To solve a system of equations, you can replace a variable with an equal value or expression.
- To check a solution, you can substitute the solutions into the equations and verify that both equations are true.
- Substitution is the best method to use when one variable is already isolated or when one variable can be easily isolated.
Let me know if you need any more information or assistance!