1)To construct the line parallel to given line passing through given point, first take a point on the line.
2)Here in the problem that point is Q.
3)Join PQ.
4)After joining PQ, copy the angle made by PQ by constructing the arc MN with steel point of compass on Q. Keep same disttance and get arc M'N' by keeping steel point on P. Then measure length MN on the angle PQR and cut arc by placing steel point on M' and cutting the arc to get point N'.
5) Join PN' and extend till point S.
6) PS is parallel to QR.