5.3.1.17 Construction of sections

condition: Construct a section of the prism \( A B C A_{1} B_{1} C_{1} \) by the plane defined by the points \( P, Q \) and \( R . P \) lies in the face \( A A_{1} B_{1} B, Q \) lies on the edge \( A C \), \( R \) lies in the face \( B B_{1} C_{1} C \).