Relevant costing – Kaplan exam kit, Q84

Please bear with me as the question is quite long but the question is simple. It’s all about shrinkage.
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Q84
Appler is considering the relevant cash flows involved in a short-term decision. An important client has asked for the minimum price for the processing of a compound. The compound involves the following:

MAT A: Appler needs 500 kg of material for the compound but has 200 kg in stock present. The stock items were bought 3 months ago for $5/kg but have suffered 10% shrinkage since that date. Material A is not regularly used in the business and would have to be disposed of at a cost to Appler of $400 in total. The current purchase price of material A is $6.25/kg.

MAT B: Appler needs 800 kg of material B and has this in stock as it is regularly needed. The stock was bought 2 months ago for $4/kg although it can be bought now at $3.75/kg due to its seasonal nature.

Processing energy costs would be $200 and the supervisor says he would allocate $150 of his weekly salary to the job in the company’s job costing system.

Based upon the scenario information, what is the total cost of MAT A and B to be built in to the minimum price calculation?
$[ _________ ]
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According to Kaplan, MAT A to be bought is 300 kg and so it arrives at $4,475 in total.
In my opinion, due to 10% shrinkage, MAT A to be bought is 320 kg, hence the total is $4,600. What am I doing wrong here Sir? I am struggling with relevant costing.

That will be all for today. Thank you very much in advance. God bless you.