Final answer:
By dividing 66m³ by 5.5m³ per day, it is determined that one can use 66m³ of water for 12 days at the given daily usage rate.
Step-by-step explanation:
To calculate for how many days one can use 66m³ of water at a rate of 5 1/2m³ a day, the total volume of water available needs to be divided by the daily usage rate. Since 5 1/2m³ can be expressed as 5.5m³, we divide 66m³ by 5.5m³ to find the number of days.
66m³ ÷ 5.5m³/day = 12 days.
Therefore, one would be able to use 66m³ of water for a total of 12 days if using 5 1/2m³ per day.