The symphony sells two kinds of tickets: orchestra, for $30, and upper tiers, for $12. On a certain night, the symphony sells 90 tickets and gets $1800 in revenue from the sales. How many orchestra tickets did they sell?
Choices.
A) 20  B) 30  C) 40  D) 50  E) 60
Let x be the number of orchestra tickets.   Then 90-x is the number of upper tier tickets.   30x + 12(90-x) = 1800   18x = 1800-1080   x = 40   The answer is 40.
<result>C</result>
The symphony sells two kinds of tickets: orchestra, for $30, and upper tiers, for $12. On a certain night, the symphony sells 90 tickets and gets $1800 in revenue from the sales. How many orchestra tickets did they sell?