we know that
The volume of a sphere (rubber ball) is equal to
[tex]V=\frac{4}{3} \pi r^{3}[/tex]
where
r is the radius of the sphere (rubber ball)
The volume in function notation is equal to
[tex]V(r)=\frac{4}{3} \pi r^{3}[/tex]
in this problem we have
[tex]V(\frac{5}{7})[/tex]
that means
The radius of the rubber ball is [tex]\frac{5}{7}\ ft[/tex]
and
The volume of the rubber ball is [tex]V(\frac{5}{7})\ ft^{3}[/tex]
therefore
the answer is the option B
the volume of the rubber ball when the radius equals [tex]5/7[/tex] feet
