Two Vending Machines Sit Side by Side in a A College

Multiple Choice

Two vending machines sit side by side in a a college dorm. One machine sells Coke products and the other sells Pepsi products. Daily sales of Coke products, based on the prices of the products in the two machines are shown in the table below. In order to estimate the sales of Coke products when the price of Coke is $0.75, which variable should be held constant?

A) no variables need to be held constant
B) the daily sales of Coke products
C) the cost of Coke and Pepsi
D) the cost of Coke
E) the cost of Pepsi