A baker is preparing the 8 trays of cookies. Each tray will have either Chocolate Chip cookies or Oatmeal Raisin cookies, but not both. Chocolate Chip cookies require 7 ounces of flour, and Oatmeal Raisin cookies require 3 ounces of flour. If $x$ is the number of trays that will be set up for Chocolate Chip cookies and the remaining trays will be set up for Oatmeal Raisin cookies, which of the following expressions represents the total number of ounces of flour required?