The Hydro water department has a monthly service charge of $15.50 and a volume charge of $1.73 for every 100 cubic feet of water. The total monthly cost is equal to the service charge plus the charge for the volume used during the month. If we let x represent the number of cubic feet of water (in hundreds) and y represent the total monthly cost, then we have:
total monthly cost = volume charge + service charge
y = 1.73x + 15.50

If the Johnson family used 300 ft3 less water this month than last month, then they can expect
an increase in their water bill of $46.50.
B.
a decrease in their water bill of $46.50.
C.
an increase in their water bill of $5.19.
D.
a decrease in their water bill of $5.19.