Tickets to a certain concert sell for $20 each. The first 10 people to show up at the ticket booth received a 40% discount, and the next 20 received a 15% discount. If 48 people bought tickets to the concert, what was the total revenue from ticket sales?  Choose the most appropriate option:
A) $ 600
B) $ 820
C) $ 850
D) $ 980
E) $ 1,140

Rationale: "price of 1 ticket = 20 $ revenue generated from sales of first 10 tickets = 10 * ( 60 / 100 * 20 ) = 10 * 12 = 120 revenue generated from sales of next 20 tickets = 20 * ( 85 / 100 * 20 ) = 20 * 17 = 340 revenue generated from sales of last 18 tickets = 20 * 18 = 360 revenue generated from sales of 48 tickets = 120 + 340 + 360 = 820 $ answer b"
Answer: B