The best possible option would be the third one. This is because, we can determine the cost or the equation to calculate the total cost Sam obtains by breaking the problem.
Sam works for 7.00 per hour and this would along with him working for 6 hours is some of the total cost.
The rate 5n represents that he earns 5.00 dollars for each person he serves, if the function is asking for the total price based on the number of people he serves it would be this.
