Tennis balls are stored in a cylindrical container with height 21 centimeters and diameter 7 centimeters. Three tennis balls fit in one container. Find the volume of the container. b. Find the volume of a tennis ball.

Step 1 ：The problem provides the diameter of the cylindrical container as 7 centimeters. The radius is half the diameter, so \(r = \frac{7}{2} = 3.5\) centimeters.

Step 2 ：The height of the cylindrical container is given as 21 centimeters.

Step 3 ：We can find the volume of the cylindrical container using the formula \(V = \pi r^2 h\). Substituting the given values, we get \(V = \pi (3.5)^2 (21)\).

Step 4 ：Calculating the above expression, we find that the volume of the container is approximately 808.1747101359742 cubic centimeters.

Step 5 ：\(\boxed{808.1747101359742}\) cubic centimeters is the volume of the container.