Cannot be answered with only these measurements. You need to specify what shape the pool is. Also, for a rectangular pool, the length, width and depth are needed. For a round pool, the diameter and depth are needed.
Twelve feet of water in a 10-foot round pool is approximately 7,080 gallons.
Exactly 5264.1669 gallons
Three feet of water in a 12-foot round pool is about 2,550 gallons.
3961
An 18-foot round pool with 3 feet of water contains 5,734.8 gallons of water. If you fill it to 4 feet deep it increases to 7,646 gallons of water.
That all depends on how deep the water has to be, which the question neglects to specify.
141.06 gallons
(3.5 feet) * PI * ((9 feet)^2) = 6 662.46122 US gallons
13,594 US gallons of water.
About 18,402 gallons.
About 24 gallons.
367.2 (rounded)