Advance tickets: $30
Same-day tickets: $20
Tickets sold: 55
Total money: $1300
Let us say that a represents the number of advance tickets sold, and s is the number of same-day tickets sold. Then, from the total number of tickets sold:
And for the total income:
From (1):
Using this result on (2):
Using this on (1'):
Number of advance tickets sold: 20
Number of same-day tickets sold: 35