The tank is a cylinder. The volume formula for a cylinder is V=pir^2h. So plug in the information.
V= (3.14)(12^2)(30)
12 squared or 12x12 is 144.
V=(3.14)(144)(30)
Multiply the 3 numbers.
13,564.8 is the product.
So the volume of the Cylindrical tank is 13,564.8.
If you are still don't understand I can help more:)