You have to find the pattern. Divide the amount of ounces by the cost to see that you are dividing by 12.5. So, 12/12.5 = 0.96. Soooo if you do 1 ounce/ 12.5 you get 0.08.
Well 13 /3 = 4.3333, that sure the cost for one book and the rate. so if he bought 12 books at the same rate, then its 12*4.33333. which equals 52 dollars
