This lesson does a great job of showing how to solve a system of 3 equations in 3 variables using the substitution method. This same problem was done in the previous lesson in this series using the elimination / addition method. The elimination method is actually used deep into this problem in 1 step because it is easier. Each step involved in this sometimes difficult process is shown. This is a great place to start to learn how to solve a system of 3 equations.