Answer: There are several information's of immense importance already given in the question. Let us write them down first.
Diameter of the cylinder = 6 inches
Then
Radius of the cylinder = 3 inches.
Height of the cylinder = 3 * radius
= 3 * 3
= 9 inches
Volume of the cylinder = (pi) * (Radius)^2 * Height
= 3.14 * (3)^2 * 9
= 3.14 * 9 * 9
= 254.34 cubic inches