firstly you need to know the equation for the circumference of a circle;
\(pi\times d\) or \(pi\times 2r\)
in this example we know that;
\(pi\times2r = 14pi\)
divide both sides by \(pi\);
\(2r = \frac{14pi}{pi}\)
simplify;
\(r = 7\)
and there you go - the radius is 7cm
