Final answer:
After deducting the service charge from the total bill, and then dividing the remaining amount by the volume charge, we find that the Sandstone family used 3,000 cubic feet of water in June.
Step-by-step explanation:
The Sandstone family's water bill includes a monthly service charge and a volume charge per 100 cubic feet of water used. To determine how much water they used, we first subtract the monthly service charge from the total bill. With a total bill of $73.10 and a monthly service charge of $6.80, we are left with $73.10 - $6.80 = $66.30 that accounts for water usage.
Next, we divide the remaining amount by the volume charge to find out how many 100 cubic feet units were used: $66.30 ÷ $2.21. This yields approximately 30 units of 100 cubic feet. Therefore, the Sandstone family used 30 × 100 cubic feet of water, which is 3,000 cubic feet.
The correct choice is D. 3,000 cubic feet of water.