Hey, I've been trying to solve these questions for hours but I keep getting the wrong answer, could you please help me out and explain to me how to solve it.

On 1 January 2019, Thyssen Corporation purchased a building for $200,000. Thyssen Corporation believes that it will use the building for 30 years. After 30 years, the building will be sold at $20,000. After consideration of accumulated depreciation, how much is the net book value of the building on the balance sheet at December 31,2020?

Jenkins Company began business in June when stockholders invested $80,000 in the business, which in turn issued its common stock to them. Jenkins Company then purchased a building for $40,000 cash and inventory for $20,000 cash, performed services for clients for $10,000 cash, purchased supplies for $5,000 cash, and paid utilities of $2,000 cash. What is the amount of Cash at the end of June?

FUZZY Company reported a balance of $6,075 million in Inventory at the beginning of 2009 and $7,200 million at the end of 2009. Its Cost of Goods Sold for 2009 is $34,050 million. How much is the cost of inventory purchased during 2009?