A jazz concert brought in $207,000 on the sale of 8,100 tickets. If the tickets sold for $20 and $30 each, how many of each type of ticket were sold?

X = 20 dollar tickets and y = 30 dollar tickets

x + y = 8100 ... x = 8100 - y

20x + 30y = 207,000

20 (8100 - y) + 30y = 207,000

162,000 - 20y + 30y = 207,000

-20y + 30y = 207,000 - 162,000

10y = 45,000

y = 45,000/10

y = 4500 < = = = there were 4500 thirty dollar tickets sold

x + y = 8100

x + 4500 = 8100

x = 8100 - 4500

x = 3600 < = = = there were 3600 twenty dollar tickets sold