3.1: Sector with an interior chord to a point on a radius

$AOB$ is a sector of a circle with centre $O$ and radius $16\text{ cm}$. Angle $AOB$ is $\dfrac{2\pi}{7}$ radians. The point $C$ lies on $OB$ such that $OC$ is of length $7.5\text{ cm}$ and $AC$ is a straight line.