This is a problem of volume. So we have the following volumes:
1. For the balls: Volume of a sphere.
[tex]V_{1s} = \frac{4}{3} \pi r^{3} = \frac{4}{3} \pi (2.7)^{3} = 82.44in^{3}[/tex]
Given that we have three balls, then the total volume of the balls is:
[tex]V_{3s} = 3\times 82.44in^{3}=247.34in^{3}[/tex]
1. For the cylindrical can:
[tex]V_{c}=\pi r^{2}h[/tex]
h is the height, that is, if the balls touch the sides, bottom and top of the canister, then it is true that:
[tex]h=6r=6(2.7)=16.2in[/tex]
The radius of the cylindrical can is the same as the radius of a ball, therefore:
[tex]V_{c}=\pi (2.7)^{2}(16.2)=371.01in^{3}[/tex]
Finally the volume of the air between the tennis balls in the can is:
[tex]V_{A}=V_{c}-V_{3s}=371.01-247.34 \rightarrow \boxed{V_{A}=123.67in^{3}}[/tex]