Nicky is considering two different companies for textbook rentals. For
what number of months will Company B cost less?
• Company A charges a one-time account fee of $20 and a rental fee of
$15 per month
• Company B charges $20 per month with no other fees.
Show your work.

All the answers except C has a Vertical Line when graphed. It must pass the Vertical line test in order to be a function.

Vertical Line Test: If you can draw a vertical line anywhere on a graph so that it hits the graph in more  than one spot, then the graph is NOT a function.

C.) can pass the test since it's a horizontal line.

Hope this helps!