1.16: Parallel chords with given arc and sector

The diagram shows a circle, centre $O$, radius $10\text{ cm}$. The points $A$, $B$, $C$ and $D$ lie on the circumference of the circle such that $AB$ is parallel to $DC$. The length of the minor arc $AB$ is $14.8\text{ cm}$. The area of the minor sector $ODC$ is $21.8\text{ cm}^2$.