Transfer pricing ( opportunity cost )

Dear John, Its the question from my sister’s Final exams of CA (India). the syllabus same,so she given me this question.

Q- Divizon Z produces the products – A , B , C , D. and each product is sold externally too.

A B C D

market price p.u – 150 146 140 130

variable cost p.u – 130 100 90 85

labour required p.u – 3 4 2 3

Product D can be transferred to division Y, but the maximum qualtity that may be required to transfer to Division Y is 2500 units of D.

The maximum sales in externam market:-

A= 2800
B= 2500
C= 2300
D= 1600

Division Y can purchase the same product at price of 125 p.u. from outside insted of receiving transfer of product D from divison Z.
What should be transfer price for each unit for 2500 units of D, if total labour is 20,000 Hours.

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SOLUTION I CALCULATED :- consider all values in $
In first attempt i got confused and ended up getting the quesstion wrong, but then by following the formula from lectures. thats how i did it. the answer was right second time but i want to know , is this right way as in her book its solved in different way ?

I calculated contribution per labour hour first.

A B C D
Contribution pu 20 46 50 45

labour hrs. pu 3 4 2 3

contribution per
labour hrs 6.67 4 25 15

so, C should be produced first , then D , then B , then A

So, the produced units if we didn’t transfer product D
Uni4ts Total hrs
C= 2300*2 = 4600
D= 1600*3 = 2800
B= 2500*4 = 10,000
A= 200*3 = 600 Total hrs.= 20,000

so, by producing 2500 extra units for divison Y.

C= 2300*2 = 4600
D=(1600+2500) * 3 = 12,300
B= 775*4 = 3100 total hrs= 20,000 & product A can’t be produced due to limited hrs

By producing Product D , We lost contribution = (200 units of A + 1725 units of B) = (200*20) + (1725*46) = 83,350

and by Producing 2500 units of D, we Gained contribution = 2500* 45 = 112,500

so, Net contribution gained / positive opportunity cost = 112,500-83,350 = 29,150

so, the net Positive Opportunity cost/ gained contribution p.u = 29,150/2500 = 11.66

Transper price = Marginal cost + lost contribution/ opportunity cost
= 85 + 45 ( contribution will be lost if not sold in market price of 130 )
+ [ -11.66 ( which is negative Opportunity cost or COntribution gained by producing D insted of A and B )

= 118.34 which is correct answer.

and IN BOOK ,

it calculated total contribution lost= 83,350 by not producin A and B and variable cost of D= 2500*85 = 212,500.

total to be recovered = 83,350+212,500 = 295,850

so, T.P = 295,850/2500 = 118.34 per unit.

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Is it likely for this type of question to come in exam ?
Also, will i get the full marks by doing the question like i did using the formula in section C ? , and also, Have i done it correctly ( By exam standards ), All shorts of doubt come in mind even i get right answer !!!

Thanks you so much for your time,i know i wrote alot, sorry for your trouble.