In 2018, firm a extracts 50,000 tons of ore, valued at $100 per ton, using previously existing machinery. firm b produces 10,000 tons of steel sheets, valued at $3,000 per ton, having bought and used all of the ore produced by firm a. firm c manufactured 5,000 vehicles and sold them all to households for $25,000 each, having purchased 8,000 tons of steel sheets from firm b. in addition, firm c imported 5,000 engines from a foreign subsidiary each valued at $5,000, and purchased 20,000 tires from firm d for $100 each. firm d produced 100,000 tires valued at $100 each, but only sold 60,000 tires during 2018. firm d purchased 2,000 tons of steel sheets from firm b since all of their tires are steel belted radials.