Answer: B) 15 mph
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Step-by-step explanation:
The equation d = 65t means that the rate is r = 65. So Malcolm's family travels at an average rate of 65 mph. Note this is the slope of the line.
The graph has a slope of 50 because each time we go up 50, we move to the right 1. Ie, slope = rise/run = 50/1 = 50. You could use the slope formula to get the same result.
Since the graph has a slope of 50, this means Theo's family is going at an average speed of 50 mph.
Subtract the two speeds to get 65-50 = 15 mph