He graph shows the distance, y, in miles, of a moving motorboat from an island for a certain amount of time, x, in hours: A graph titled Distance Vs. Time is shown with Time in hours labeled on x axis and Distance from Island in miles labeled on y axis. The scale on the x axis shows the numbers 1, 2, 3, 4, 5, 6, 7, and the scale on the y axis shows the numbers 0, 35, 70, 105, 140, 175, 210, 245, 280, 315. The graph shows a straight line joining the ordered pairs 0, 35, and 1, 105, and 2, 175, and 3, 245, and 4, 315.
What is the speed of the motorboat? (5 points)

35 miles per hour
70 miles per hour
105 miles per hour
315 miles per hour