Steps of construction:
- Draw an angle ABC of 108°.
- With B as the center and any radius draw an arc which intersects AB at P and BC at Q.
- With P as center and radius more than half of PQ draw an arc.
- With Q as the centre and same radius draw an arc which intersects the previous arc at R.
- Join BR.
Therefore $\angle\text{RBC}=60^\circ$


