Inventory

Hi. Can you please explain this question to me about inventory valuation.
It is my understanding that inventory is valued at the lower of cost & NRV. NRV is calculated by deducting the cost of completion, costs to sell from the selling price.

So please explain why the cost of completion (33600) is not deducted from the contract price ($36000) along with the extra cost of 4200 (8400/2).

Q.)Neville has only two items of inventory on hand at its reporting date.

Item 1 – Materials costing $24,000 bought for processing and assembly for a customer under a ‘one off’ order which is expected to produce a high profit margin. Since buying this material, the cost price has fallen to $20,000.

Item 2 – A machine constructed for another customer for a contracted price of $36,000. This has recently been completed at a cost of $33,600. It has now been discovered that in order to meet certain health and safety regulations modifications at an extra cost of $8,400 will be required. The customer has agreed to meet half of the extra cost.

What should be the total value of these two items of inventory in the statement of financial position?

Thank you!