Hello, my name is Natalie. Thank you for the opportunity to help you with your question!
To figure this out first you need to remember the area equation for a circle which is pi*r squared
pi * 27^2 = 2290.221044 ft^2
Then you need to convert 400,000 gallons into ft^3
This is done by dividing 400,000 gallons by 7.48 gallons
this equals 53475.93583 ft^3
Since the volume of a cylinder equals the area of the top (area of the circle we determined) multiplied by the height you can set
53475.93583 ft^3 = 2290.221044 ft^2 * h
divide by 2290.221044 ft^2 on both sides
h = 23.349683 ft
Since the smallest number of significant figures is 3 the answer would therefore be h = 23.3 (the 4 rounds down)
Please let me know if you need any clarification. If you do, please message me in a chat, as I will not be notified if you responded here to the problem. I'm always happy to answer your questions. Thank you again for giving me the opportunity to be your tutor!