For <em>company</em><em> A</em>, you are multiplying 20 by h because you must pay $20 per hour. Then, you have to add 100 to that because there is a $100 dollar rental fee.
For <em>company </em><em>B</em>, you are multiplying 40 by h because you must pay $40 per hour. There is no rental fee, so that means you don't have to add anything.
The plot shows (1, 1) and (1, 3) are both defined by the relation. It does not pass the "vertical line test", which requires the relation be single-valued everywhere.
