A farmer has 500 acres of land to plant 4 crops—wheat, corn, soybeans, and tomatoes. The different types of crops vary in how many gallons of water they use per acre and how much worker time (in hours) they need per month for each acre. The farmer wants to determine the acres of land to use to plant each crop in order to have the least water usage per month. Given the limited number of workers available, there is a total of 800 worker hours available each month. You do not need to solve this problem algebraically or in Excel. Answer the following question in words only. Describe "in words only" (including the unit) as to what are the decision variables of this problem.