This is to also make sure people are confident in doing these problems. We need to know how to work these problems for the future references. We need to know how to do these problems for college level math and graduate school, if you decide to go.
Substitution is the method of solving one equation for x or y to find the answer to both equations.
Solve to find one variable. Then resubtitute to find the other equation. The first is deciphering which equation is all ready to be substituted in which equation. The third step is to solve the equation. This method is a very simple method of guess and check.