It is to be noted that most of the products we have now in the market are sold per volume or per area. For example, when we buy olive oil, we buy by the volume. Example, 250 mL, 1 L, and so on. In the surface area as well, when we buy boxes, it can be directly concluded that bigger boxes will have to be more expensive than the smaller ones.
3 days. If every day he runs 10 laps then that would be 4000 meters. 1 kilometer is equal to 1000 meters. That means everyday he runs 4 kilometers. Then after 3 days he would have ran 12 kilometers.