Betty gives piano lessons. She has an opportunity cost of $50 per lesson and charges $60. She has two students: Archie, who has a willingness to pay of $70, and Veronica, who has a willingness to pay of $90. When the government puts a $20 tax on piano lessons and Betty raises her price to $80, the deadweight loss is _________ and the tax revenue is _________.

a. $10; $20

b. $10; $40

c. $20; $20

d. $20; $40