4. As shown in Figure 6, in $\triangle A B C$, two line segments $B Q$ and $C R$ intersect at point $P, A R=B R=C P, P Q=C Q$. Find the degree measure of $\angle B R C$.

保留了源文本的换行和格式。
(Tip: On the extension of $CR$, take $RK=RC, RS=PC$. It is easy to get $\triangle BSK \cong \triangle BRP, BS=BR=CP=SR$. Therefore, $\triangle BRS$ is an equilateral triangle, $\angle BRS=60^{\circ}, \angle BRC=120^{\circ}$.)