Since the same person cannot hold more than one position, the company has 15 options for the first choice, 14 for the second choice and 13 for the third choice, and since the three chosen positions are different, the order of the picks also matter. The number of ways the selection can be made is:
If you multiply the price for each mule x the amount of miles + the daily rental, you get the price. If you do this for each option and each car rental then you can see when the answers add up.