Suppose that there are two types of tickets to a show: advance and same-day. The combined cost of one advance ticket and one same-day ticket is $40. For one performance, 30 advance tickets and 20 same-day tickets were sold. The total amount paid for the tickets was $1050. What was the price of each kind of ticket?

This is a system
x is the number of advanced tickets sold
y is the number of same day tickets sold
once you label your variables then write the equations
x+ y = 45 total tickets sold
20x + 25y = 1050 money taken in
multiply the top equation by -20 and the x will drop out
-20x - 20y = -900
20x + 25y = 1050. Add the equations result is
5y = 150, divide by 5 ,
y or same day tickets cost $30
substitute 30 into first equation
x + 30 = 45 therefore x = 15