参考下图。QR和QP已经画出。

1. Construct the line on which $S$ must lie using the given angle at $R$.

At $R$, construct an angle of $110^\circ$ with arm $RQ$. Draw the ray from $R$ on the required side of $QR$ so that
$\angle QRS=110^\circ$.
Point $S$ must lie on this ray.

2. Locate $S$ using the given length $PS=7\text{ cm}$ and complete the quadrilateral.

With centre $P$ and radius $7\text{ cm}$, draw an arc to intersect the ray from $R$.
Choose the intersection point $S$ for which $\angle PSR$ is acute.
Join $P$ to $S$ and $R$ to $S$ to complete quadrilateral $PQRS$.

1. Construct equal arcs from $P$ and $Q$ and draw the perpendicular bisector.

Set the compass radius to more than half of $PQ$. With centre $P$, draw arcs on both sides of $PQ$. Using the same radius and centre $Q$, draw arcs to intersect the first pair of arcs. Join the two arc-intersection points with a straight line. This line is the perpendicular bisector of $PQ$.