Can anyone help a friend out?

Amount of Dollars per month.

Step-by-step explanation:

The slope is a ratio between dollars, and number of months, so the slope would be the amount of dollars per month

I am thinking C
Why? Because for every 3 hours Brook drove 180 mile so divide it by 3 and you get how many miles she drove for 1 hour. Same goes for Diederick for every 4 hours he drove 160, so divide 160 by 4 to get miles per 1 hour. You must subtract to find the difference between the two, subtracting is a great way to compare numeric values. Hope this helped!