Part A:
y = 30x + 13
y is the total cost
30 is the price per mattress
x is the number of mattress(es)
13 is the service
y = 28x + 15
y is the total cost
28 is the price per mattress
x is the number of mattress(es)
15 is the service charge
For Part B - replace the x's with 4 so for Company A
y = 30(4) + 13
30 * 4 = 120 + 13 = 133
Replace the x's with 4 so for Company B
y = 28(4) + 15
28 * 4 = 112 + 15 = 127
Company B charges less for the cleaning of 4 mattresses
Same thing for Part C, plug 7 into the x's
y = 30(7) + 13
30 x 7 = 210 + 13 = 223
y = 28(7) + 15
28 * 7 = 196 + 15 = 211
Since you are trying to find money saved from using the services of Company B to Company A, subtract total cost of 7 mattresses from Company A to Company B
233 - 211 = 22
TLDR:
Part A:
Company A: y = 30x + 13
Company B: y = 28x + 15
y = total cost
30 and 28 = price per mattress(es)
x = how many mattresses
13 and 15 = service charges
Part B:
Company A: y = 30(4) + 13 = 30 * 4 = 120 + 13 = 133
Company B: y = 28(4) + 15 = 28 * 4 = 112 + 15 = 127
Company B costs less for 4 mattresses
Plug 4 into x since you are trying to find the price of 4 mattresses
Part C:
Company A: y = 30(7) + 13 = 30 x 7 = 210 + 13 = 223
Company B: y = 28(7) + 15 = 28 * 7 = 196 + 15 = 211
233 - 211 = 22
Plug 7 into the x's because you're trying to find the price of 7 mattresses
Subtract Company B from Company A to find the cost of savings