1. You have that the diameter of the spherical tank is diameter of 30 feet. Then, you must apply the formula for calculate the volume of a sphere:
V=4πr³/3
r=30 feet/2
r=15 feet
2. The volume of the tank is:
V=4πr³/3
V=4π(15 feet)³/3
V=42,411.50 feet³/3
V=14,137.16 feet³
3. The water weighs approximately 62 pounds per cubic foot , then:
1 foot³-------62 pounds
14,137.16---x
x=876,504.35 pounds/foot³
The answer is: 876,504 pounds/foot³