(a)
The formula for circumference is
[tex]2\pi \: r[/tex]your radius is 4mm so
[tex]2 \times \pi \times 4mm[/tex]
which equals to
[tex]8\pi \: mm[/tex]
(b) type
[tex]8\pi[/tex]
in your calculator and round it off to the nearest hundred
this should be the answer: 25.133 mm
