For Part b), i am getting stuck, i take it you have to start at the voltage divider and try and work out R2. I have started this with the equation

\( V_{REF} = (\frac{R2}{R1 + R2} ) * V_{cc} \)

which re-arranges to

\( R2 = (\frac{V_{REF}}{V_{cc}} - 1) * V_{cc} \)

With Vcc being the voltage supply to the OP AMP which isn't supplied.

I have read that the value of R2 can also be given by the

\( R2 = \frac{V_{fb}}{I_{r1/2}} \)

With V_fb being the voltage to the non inverting input of the OP AMP, but also the current is not supplied for the equation. The current being the current going into R1 at the top of the voltage divider.

I am a little bit stuck, if anyone can point me in the right direction. Hopefully it is something simple i am missing! Or if i haven't explained myself very well!

Thanks for your help