



 
Hi Abigail, My first question on seeing this problem was what units do I use. I decided to use feet and then convert the depth in feet to inches. There are 5280 feet in a mile so 51.6 square miles times a depth of $d$ feet is $5280^2 \times 51.6 \times d$ cubic feet. Type 1 gallon in cubic feet into Google to obtain the number of cubic feet in a gallon and then multiply by 7 million to obtain the average daily water usage in cubic feet. What is the overlade yearly water usage in cubic feet? Solve for $d.$ Penny  


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