The graph shows the distance a car traveled, y, in x hours:
 A coordinate plane graph is shown. The x-axis is labeled time in hours ,and the y-axis is labeled distance in miles. The line passes through the points 2 comma 60, and 4 comma 120.
 What is the rise-over-run value for the relationship represented in the graph? (4 points)
 a
 20
 b
 30
 c
 1 over 20
 d
 1 over 30