Astadium has 10,000 seats, divided into box seats, lower-deck seats, and upper-deck seats. box seats sell for $10, lower-deck seats sell for $8, and upper-deck seats sell for $5. when all the seats for a game are sold, the total revenue is $70,000. the stadium has four times as many upper-deck seats as box seats. find the number of lower-deck seats in the stadium.