we know that
[volume of a sphere]=(4/3)*pi*r³
length of a circumference=42 ft
[length of a circumference]=2*pi*r-------> r=[length of a circumference]/(2*pi)
r=[42]/(2*pi)---------> r=6.6845 ft
[volume of a sphere]=(4/3)*pi*6.6845³-----------> 1251.11 ft³
the answer is 1251.11 ft³