Three tennis balls are stored in a cylindrical container with a height of 8 inches and a radius of 1.43 inches. The circumference of a tennis ball is 8 inches. Round your answers to the nearest hundredth.

the complete question is
Three tennis balls are stored in a cylindrical container with a height of 8 inches and a radius of 1.43 inches. The circumference of a tennis ball is 8 inches. a) Find the volume of a tennis ball b) There are 3 tennis ball in the container Find the amount of space within the cylinder not taken up by the tennis balls. Round your answers to the nearest hundredth.

Part a) 

we know that
length of a circumference=2*pi*r----------> r=length/(2*pi)---> 8/(2*pi)
r=1.27 in------> radius of tennis ball

volume of a tennis ball is equals to the volume of a sphere
[volume of a sphere]=(4/3)*pi*r³----> (4/3)*pi*1.27³---> 8.58 in³

the answer Part a) is
the volume of a tennis ball is 8.58 in³

Part b)
[volume of the container]=pi*r²*h-----> pi*1.43²*8----> 51.39 in³

[volume of 3 tennis balls]=8.58*3-----> 25.74 in³

the amount of space within the cylinder not taken up by the tennis balls is
51.39-25.74-----> 25.65 in³

the answer Part b) is
25.65 in³