Let b be the initial amount of books. Steve sells half of his books, so the number of Steve's books become

Then, he buys 6 more, so the number increases by 6:

This number is now 14, so you have

Subtract 6 from both sides:

Multiply both sides by 2:

In short you just multiply 0.480.48 by the amount of miles you drive add that to 24.9024.90 and you get you total
for example: if you take the first company if you drive 200 miles per day it will cost you 24.9024.90 with an extra 96.096 wich will add up to 120.99849 in total per day
20% decrease should be the answer
13 packs of meat patties and 16 packs of buns