Hello, please help me understand the following exercise:

18. Following are the demand, total revenue, marginal revenue, total cost and marginal cost schedules (All in $) for a monopolist publisher of a textbook in Microeconomics.

Number of books per hour	Price	Total Revenue	Total Cost	Marginal Revenue	Marginal Cost
0	8		12
1	7		15
2	6		17
3	5		20
4	4		24
5	3		29

When the monopolist publisher maximizes its profits, what would be his total profit ($) per hour?

19. Following are the demand, total revenue, marginal revenue, total cost and marginal cost schedules (All in $) for a monopolist publisher of a textbook in Microeconomics.

Number of books per hour	Price	Total Revenue	Total Cost	Marginal Revenue	Marginal Cost
0	8		12
1	7		15
2	6		17
3	5		20
4	4		24
5	3		29

When the monopolist publisher maximizes its profits, what would be his total cost ($) per hour?

20.Following are the demand, total revenue, marginal revenue, total cost and marginal cost schedules (All in $)for a monopolist publisher of a textbook in Microeconomics.

Number of books per hour	Price	Total Revenue	Total Cost	Marginal Revenue	Marginal Cost
0	8		12
1	7		15
2	6		17
3	5		20
4	4		24
5	3		29

If the monopolist publisher shuts down and prints no books, how much money does he lose ($) ?