Quandaries
and Queries 

Who is asking: Student Question: Thanks a lot. I really need some help :) 

Hi John, There is more than one way to solve these sysyems of equations, but since the subject line of your email was "substitution method" let's use that method. The first system is
For the substitution method you want to use one of the equations to find an expression for one of the variables, either a or b. I am going to use the second equation to find an expression for b.
Now that I have an expression for b I will substitute it into the other equation, in this case the first equation
This equation has only one variable, a, so you can simplify and solve for a.
If you substitute this value for a back into either of the original equations you can then solve for b. Make sure you check your answer when you are done. For your second system of equations I would solve the first equation for b and then substitute into the second equation. Cheers, 

