7. You are planning a camping trip. The campsite you want to rent charges a $15 fee to reserve the site, plus an extra $3 per day. Part I: Define your variables and write a linear equation in slope-intercept form to represent the cost of the campsite. (4 points) Part II: Find the y-intercept and interpret it. (2 points) Part III: Graph the equation for the cost of renting the campsite. Label three points on your graph and indicate the slope. (5 points)