I1.2 In Figure 1, $A D$ and $B E$ are straight lines with $A B=A C$ and $A B / / E D$. If $\angle A B C=R^{\circ}$ and $\angle A D E=S^{\circ}$, find the value of $S$.
$\begin{array}{ll}\angle A B C=30^{\circ}=\angle A C B & \text { (base } \angle \text { isos. } \triangle \text { ) } \\ \angle B A C=120^{\circ} & (\angle \mathrm{s} \text { sum of } \triangle \text { ) } \\ \angle A D E=120^{\circ} & \text { (alt. } \angle \mathrm{s} A B / / E D \text { ) } \\ S=120 & \end{array}$