A hire firm charges 50 dollars a day plus 10 cents a mile. Which part is the fixed cost?

1. A variable cost is multiplied by the unknown quantity, so it changes as that quantity changes. 2. The 10 cents a mile is multiplied by the miles driven, so it is the variable cost. 3. The 50 dollars a day does not depend on the miles at all, so it is added on as a fixed cost. 4. The model is therefore total cost equal to 0.10 times miles plus 50. _Source: OpenStax College Algebra (CC BY 4.0), section 2.3 Models and Applications_