There were 27,000 people at a ball game in los angeles. the day's receipts were $204,000. how many people paid $13 for reserved seats and how many paid $6 for general admission?

21000 people paid for general admission and 6000 paid for reserved seats. This is solved by making 2 equations. Out of 27000 people who were at game, x of them paid for general admission and y for reserved seats, thus
x + y = 27000
As said, daily receipts were 204000$. As reserved seat is 13$, y of them gave 13$ each (y*13$) and x of them gave 6 for general admission(x*6) and those two add up and we get second equation
13y + 6x = 204000.
This can be solved by transforming first equation into x = 27000 - y and then replacing the x in second.
13y + 6*(27000 - y) = 204000
13y + 162000 - 6y = 204000
7y = 42000
y = 6000
x + 6000 = 27000
x = 27000 - 6000 = 21000