The circumference of a circle can be found by the formula
[tex]S=2\cdot\pi\cdot r[/tex]this can also be written in function of the diameter
[tex]S=\pi\cdot D[/tex]From this formula we can find the diameter
[tex]D=\frac{S}{\pi}[/tex]Using the information given, the diameter of the circle is
[tex]D=\frac{21.98}{\pi}=6.996\approx7ft[/tex]