Systems of linear equations:

Based on our practice PARCC. I suggest reviewing the following lesson on Khan Academy:

https://www.khanacademy.org/math/high-school-math/algebra/algebra-functions/recognizing-functions-ddp/v/graphical-relations-and-functions

https://www.khanacademy.org/math/high-school-math/algebra/algebra-functions/recognizing-functions-ddp/v/graphical-relations-and-functions