Problem #PRU-5166

Problem

Given two circles, one has centre $A$ and radius $r$, another has centre $C$ and radius $R$. Both circles are tangent to a line at the points $B$ and $D$ respectively and the angles $\mathrm{\angle }CED=\mathrm{\angle }AEB={30}^{\circ }$. Find the length of $AC$ in terms of $r$ and $R$.