For every 24 cookies Markes needs 2.5 cups of flour. So, for 12 cookies he needs half of that which is 1.25 cups. 12 is a fifth of 60, so we multiply 1.25 by 5 which gives us 6.25 cups of flour. :D
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.