A suitable calculator or spreadsheet can find the matrix product for you. Here, the answer choices differ in their upper left term, so we can determine the correct choice by finding the value of that term. It is the dot product of the first row of B and the first column of A.
You save 5 cents per ounce by using the 40 ounce jar, because if you do $5.20 divided by 40 it equals $0.13 but if you do $2.70 divided by 15 it equals $0.18 which is 5 more cents the the 40 ounce
