65.9 cm
Step-by-step explanation:
The formula for the circumference of a circle is...
[tex]C=\pi d[/tex]
Since the problem asks to round to the nearest tenth, we know that we will convert pi to 3.14. We also know the diameter is 21, so we can put both of these in the formula.
[tex]C=3.14*21[/tex]
C = 65.940
Rounded to the nearest tenth...
C = 65.9 cm
