Can anybody help regarding the question below? TIA

You bargain with X over a share of £100. There are 3 offer-counteroffer rounds. In each round:

a) You make an offer to Z
b) Z accepts or rejects it
c) If Z rejects, he makes a counteroffer
d) You accept or reject the counteroffer

Each time an offer is rejected, £5 are subtracted from the prize. If the last offer is rejected (i.e., the total of £30 is lost after 6 rejections) you get £20 and Z gets £50.

Explain and show the analysed game, finding relevant game theoretical solutions.