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 $1620 in revenue from the sales. How many orchestra tickets did they sell?	Choose one.
A) 25  B) 30  C) 35  D) 40  E) 45
Let x be the number of orchestra tickets.   Then 90-x is the number of upper tier tickets.   30x + 12(90-x) = 1620   18x = 1620-1080   x = 30   The answer is 30.
<result>B</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 $1620 in revenue from the sales. How many orchestra tickets did they sell?