Maria can read $20$ pages of economics in an hour. She can also read $50$ pages of sociology in an hour. She spends $5$ hours per day studying.

a$.$ Draw Maria's production possibilities frontier for reading economics and sociology $($economics in the vertical axis$).$

bb$.$ What is Maria's opportunity cost of reading $1$ page of sociology?

c$.$ What is Maria's opportunity cost of reading $100$ pages of sociology? $($compute it using $2$ different ways.$)$