4. When Mercator Manufacturing Inc. checked its stores, it had the following inventory on hand as at December 31, 2015:

a) 5,000 litres of lubricating oil that had cost $2.50 per litre: As at December 31, the replacement price was $3.00 per litre.

b) 50,000 kg of steel that had cost $0.50 per kg: As at December 31, the replacement price was $0.48 per kg.

c) Spare parts that had cost $25,000: Mostly for production machinery that was no longer in use, so it was unlikely they could be used. They have no resale value.

d) A replacement control unit for a customer's milling machine which has a resale value of $10,000: The control unit was bought by the customer so that Mercator could use it to repair their milling machine.