Radius is 17mm find the circumference?

The circumference of a circle is the circle's diameter times pi.

Also, the diameter of a circle is twice as big as the radius.

Now we have a formula!

$$C=2r\times{\pi}$$

$$C=2(17)\times{\pi}$$

$${\mathtt{C}} = {\mathtt{34}}{mm}{\mathtt{\,\times\,}}{\mathtt{\pi}} \Rightarrow {\mathtt{C}} = {\mathtt{106.814\: \!150\: \!222\: \!052\: \!970\: \!1}}{mm}$$

 

So that's our circumference.

or, rounded to the nearest tenth, 106.8mm