Grain is stored in cylindrical structures called silos which is the best estimate for the volume of a silo with a diameter of 12.3 feet and a height of 25 feet

Volume of a cylinder = base x height
the base is the area of the circle at the bottom. 

To find the area of a circle, you use:
A = πr²
where r is the radius of the circle. 
radius is half of the diameter, so with a diameter of 12.3, (divide that by 2) the radius of the circle is 6.15 feet. 

A = π(6.15)²
A ≈ 118.82 

Since we know the height is 25 feet, we can solve for the area of the cylinder. 

Area of the cylinder = 118.82 x 25 = 2,970.57 feet cubed