Which company would charge less for cleaning 4 mattresses justify your answer

The answer fam is Part A: Company A: y=30x+13 Company B: y=28x+15

X: number of mattresses

Y: total cost

Part B:

Company A: 30 (4) + 13 = 133 Company B: 28 (4) + 15 = 127

Company B cost less than Company A does when you purchase 4 mattresses

Part C:

Company A: 30 (7) + 13 = 223

Company B: 28 (7) + 15 = 211

You save $12 by using the services of Company B instead of Company A to clean 7 mattresses