The graph shows the distance y, in miles, of a moving train from a station over a certain period of time, x, in hours:What is the speed (in miles per hour) of the train and why? 80 miles per hour, because speed is the initial value of the function 120 miles per hour, because speed is the distance traveled in unit time 240 miles per hour, because speed is the distance traveled in a certain time 40 miles per hour, because speed is the rate of change of distance

Answer: 40 miles per hour, because speed is the rate of change of distance

So its choice D

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Explanation:

Notice how each time x goes up by 1, y increases by 40

So the slope is 40/1 = 40

slope = (change in y)/(change in x)

or we can use the slope formula to get the same thing
m = (y2-y1)/(x2-x1)
m = (120-80)/(1-0)
m = 40/1
m = 40
I used the two points (0,80) and (1,120) for the slope formula, but you can use any two points you want as long as they lie on the diagonal line