This document discusses the substitution method for solving systems of equations. It provides two examples of using this method. The substitution method involves: (1) defining variables, (2) writing a system of equations, (3) substituting the value of one variable into another equation to eliminate that variable, (4) solving the resulting equation for the remaining variable, and (5) substituting this value back to find the first variable. This allows the system to be solved to find the values of both original variables.