3.24: Tangent and obtuse central angle

In this question all lengths are in metres.

The diagram shows a circle, centre $O$, radius $7$. The points $A$ and $B$ lie on the circumference of the circle. The line $BC$ is a tangent to the circle at the point $B$ such that the length of $BC$ is $24$. The length of the minor arc $AB$ is $12.25$.