we know that
The volume of a sphere is equal to
V=(4/3) pi r^3
In this problem we have
D=3.6 ft
REmember that
The diameter is two times the radius
so
r=D/2
r=3.6/2
r=1.8 ft
assume the value of pi=3.14
substitute the given values
V=(4/3)(3.14)(1.8^3)
V=24.4 ft^3