Mabel is comparing the prices of two car rental companies. Company A charges $35 per day and an additional $15 as service charges. Company B charges $42 per day and an additional $10 as service charges. Part A: Write an equation to represent each company's total charges for renting a car for a certain number of days. For both equations (one for Company A and one for Company B), define the variable used.

Part B: Which company would charge less for renting a car for 6 days? Justify your answer.

Part C: How much money is saved by using the services of Company A instead of Company B to rent a car for 10 days?