The graph shows the distance, y, in miles, of a moving motorboat from an island for a certain amount of time, x, in hours:
what is the speed of the motorboat?
35miles per hour
70 miles per hour
105 miles per hour
315 miles per hour

Speed can be defined as the ratio of Change in Distance and Change in Time
i.e
Speed = (Change in distance) / (Change in time)

Since the graph is a straight line, we can consider any interval to calculate the speed as for a Linear graph the change remains the same.

From the graph we can see that at 1 hr the distance covered is 105 miles and at 2 hr the distance covered is 175 miles.

Change in Distance = 175 – 105 = 70 miles
Change in time = 2 – 1 = 1 hour

So, the speed is = 70 mile/1 hour = 70 miles per hour.

So option B gives the correct answer