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 $1980 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) = 1980   18x = 1980-1080   x = 50   The answer is 50.
<result>D</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 $1980 in revenue from the sales. How many orchestra tickets did they sell?