A sphere with a diameter of 9 units fits exactly in the clear glass cube as shown. Which expression represents the volume, in cubic units, of empty space in the cube?

Volume of a sphere: (4/3) (pi) (r^3)

r=4.5, if 9 is diameter

Volume of sphere: (4/3) (pi) (4.5) ^3

=121.5pi

Volume of cube: (s) ^3

s=9

=729

729 (volume of cube) - 121.5 (volume of sphere) = 607.5 units of empty space