I don't usually struggle with maths, but if anybody could help me, it would be appreciated again!

The length of an arc of a circle is 12cm. The corresponding sector area is 108cm squared. Find:

a) the radius of the circle.

b) the angle subtended at the centre of the circle by the arc.

See attached and check if I have drawn the correct diagram.

Help is much appreciated again,

Thanks

D Loizou