The image is attached to this link https://i.stack.imgur.com/oVfOR.png 1. What is the working out to find "b"? I understand that I need to find an angle in the triangle but what steps can I take to first of all get an angle in the triangle? From this, I will be able to use trig to find b.
The circumference of the sector $s = r \theta$, where $\theta$ is in radians. Since you know both $s$ and $r$ you can find $\theta$.