Is quadrilateral $ABCD$ a convex or concave quadrilateral.

A circle is inscribed in quadrilateral ABCD, touching sides AB, BC, CD and DA at P, Q,R and S, respectively. If $\mathrm{As}=6\mathrm{cm},$ $\mathrm{BC}=12\mathrm{cm}$ and $\mathrm{CR}=5\mathrm{cm}$, then the length of AB (in cm) is

Let $ABCD$ be a square. An arc of a circle with $A$ as centre and $AB$ as radius is drawn inside the square joining the points $B$ and $D$. Points $P$ on $AB, S$ on $AD, Q$ and $R$ on arc $BD$ are taken such that $PQRS$ is a square. Further suppose that $PQ$ and $RS$ are parallel to $AC$. Then, $\frac{\text{ area }PQRS}{\text{ area }ABCD}$ is

The three angles of a quadrilateral are $76°, 54° \mathrm{and} 108°$. Find the measure of the fourth angle.

The angles of a quadrilateral are in the ratio $3:5:7:9$. Find the measure of each of these angles.