Final answer:
The total cost for the service of a freight company with an $80 flat rate and $4 per mile is represented by the equation 'C = 4d + 80,' making option b the correct choice.
Step-by-step explanation:
The total cost for a freight company that charges a flat rate of $80 plus $4 per mile can be calculated using a simple linear equation. The cost depends on the distance traveled, d miles. According to the information provided, the total cost, C, can be expressed as:
C = 4d + 80
This equation shows that for every mile traveled, $4 is added to the initial flat rate of $80. So, if we want to represent the total cost as a function of the distance, the correct expression would be option b, 4d+80.