To find the volume of the water tank, we can use the formula for the volume of a sphere, which is V = (4/3)Οr^3, where r is the radius of the sphere.
Given that the diameter of the sphere is 5.5 feet, we can calculate the radius as half of the diameter, which is 5.5 feet / 2 = 2.75 feet.
Plugging this value into the volume formula, we get: V = (4/3)Ο(2.75^3) = 39.04 Ο cubic feet.
Since we know that 1 cubic foot is about 7.48 gallons, to find the number of gallons held in the tank, we need to multiply the volume in cubic feet by 7.48.
Therefore, the amount of water the tank holds is approximately: 39.04 Ο * 7.48 gallons.
Calculating this, the tank holds approximately: 291.3 gallon.
Therefore, the closest option to this answer is: 291.3 gallons, which is not listed in the given options.