Hi Martha,
I know that there are 231 cubic inches in an American gallon so I will change all your measurements to inches. There are 12 inches in a foot so the depth of water in the well is
12 8 = 96 inches.
The volume of a circular cylinder is r^{2} h where r is the radius and h is the height. Thus the volume of water in your well is
r^{2} h = 15^{2} 96 = 67858 cubic inches.
There are 231 cubic inches in a gallon so this is
^{67858}/_{231} = 294 gallons.
Penny
