The circus sells two kinds of tickets: lower seats for $30 and upper seats for $20. On a certain night, the circus sells 80 tickets and gets $2100 in revenue from the sales. How many tickets for lower seats did they sell? Choose the most appropriate option
A) 40	B) 45	C) 50	D) 55	E) 60
Let L be the number of lower seat tickets.   Let U be the number of upper seat tickets.   L + U = 80 and U = 80-L.   30L+20U=2100.   30L+20(80-L)=2100   10L+1600=2100.   10L=500.   L=50.   The answer is 50.
<result>C</result>
The circus sells two kinds of tickets: lower seats for $30 and upper seats for $20. On a certain night, the circus sells 80 tickets and gets $2100 in revenue from the sales. How many tickets for lower seats did they sell?