Data question - Big Book Test 25

Hi! I have a question regarding the second chart from test 25. I did watch greg’s video and I’m still not sure about this chart. In the video, Greg realized that the costs stated in the chart were for a 4 year period while solving question 24 and so, we have to divide the value of the costs by 4 if we wanted the cost per year. If that is the case, then for Q 21 how come we didn’t divide those value by 4? Q 21 asks us for the difference between the average purchase price of a standard car and a compact car. We merely took the values from the chart 8000-5600 and concluded that the answer was B - 2400. (And it is the correct one according to the answer key)

But if the values are for 4 years, then would the cost of “purchase price” for each of this car need to be divided by 4 too? Like how do I know that that cost needn’t be divided.
If I divide those two costs by 4, that is 8000/4 & 5600/4, then the difference is 600 (answer A)

Please help!
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