The circumference of any circle is (pi) x (the diameter of the circle).
The problem gives you both numbers, so all you have to do is multiply them.
Circumference = (pi) x (diameter) = (3.14) x (21cm) = <em>65.94 cm .</em>
http://lianmath.com/describe-a-serie-of-shifts-that-translates-the-graph-yx-93-4-back-onto-the-graph-of-yx-3/
Ok to solve this just write it out how it sounds, like so.
3x/4

-16
Hope this helps!=)