A roofer charges $60 for the first hour of a service call and $20 per hour for each additional hour, as shown on the graph below. Plumber's Prices 140 Price in dollars) 120 100 80 (3, 100) 60 (1, 60) 40 20 1 2 3 4 5 6 7 Hours Look at the above Roofer's Prices graph and then answer the following questions. Part A What is the slope of a line jolning the points on this graph? Show your work or explain your answer. Part B What does the slope represent?​