Final answer:
The expression for the cost of using the Easy Prep Catering company for x number of people is C = 300 + 18x, where $300 is the flat fee and $18 is the per person charge.
Step-by-step explanation:
The cost of using Easy Prep Catering company can be represented by a linear equation where the independent variable is the number of people and the dependent variable is the total cost. The flat fee is a constant and the per person charge is the variable cost. The expression that represents the cost (C) for x number of people is:
C = 300 + 18x
Here, $300 is the flat fee and $18 is the charge per person. The variable x represents the number of people, and the expression shows how the total cost changes in relation to the number of people.