Transfer pricing

Hello sir
I am referring to question 284(CTD) part b of Kaplan revision kit.
I am writing all relevant facts.
Divisions:
FD – transfering
TM – buying

Target RI calculated RI
FD. 85000. 0
TM. 105000. 180000

No. Of units transferred- 15000
Transfer price- 66
Target must be completed for bonus equal to 5% of RI. and both manager want to receive required targets.
Calculate
TM- max TPrice
FD-. min TPrice
What they did I was completely unable to understand why they did in such way.
Ans max 71
Min 71.67
If you have any other way to ans please refer to question.
Thank you sir.