



 
Hi Kimberley, What you are missing is the volume of the tank in cubic feet. Google can help with that. Type 1 gallon in cubic feet into the Google search window and the response is that 1 gallon is 0.133681 cubic feet. How many cubic feet are in 2 million gallons? If the height is 30 feet then you can use the volume formula to solve for $r.$ I hope this helps,  


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