Solving Systems of Equations by Substitution

Now that we are experts at graphing lines and determining the point of intersection, we tried a new method that might take less time. This method is the substitution method, and it is well described in the video found at this web site:
http://www.khanacademy.org/video/solving-systems-by-substitution-1?topic=core-algebra
It is also described in Investigation 4.3 of your SOA book.

Tonight's Homework: SOA ACE 4 (8 - 20). Be sure to include check steps for problems 15 - 20.