Final answer:
To set up a linear model representing the cost of buying this countertop, use the equation C = 48x + 900, where C represents the cost and x represents the number of square feet.
Step-by-step explanation:
To set up a linear model representing the cost of buying this countertop, you need to consider the cost per square foot and the base pay to install the countertop. Let's use the variable 'C' to represent the cost and 'x' to represent the number of square feet.