amplifier question

hello,
would like some help with the following question.

an amplifier with a gain of 8 has 10% of its output fed back to the input. Determine the gain of the stage with a) negative feedback and b) positive feedback.

ive read my books and cant seem to shed any light on where to start with this. can someone please point me in the right direction.
thanks keith

 

This might help:
http://en.wikipedia.org/wiki/Feedback_amplifier

Remember to multiply your own B*Vout by 0.10

For positive feedback, Vin' = Vin + B*Vout... again, your problem attenuates B*Vout to 10%.