I have to explain the vertical line test and how it is used.

Answer 1

See:
http://en.wikipedia.org/wiki/Vertical_line_test

If you need further explanations, please post.

Answer 2

Have to explain how to use a graph to determine the number of solutions system.

Am lost on what they want.

Answer 3

There was a response for you in case you did not check back:
http://www.jiskha.com/display.cgi?id=1299626093