Set up two equations: one for the amount of money collected, and one for the number of tickets sold (people who attended).
Let a= adults
Let s= students
Money equation:
[tex]15480=12a+6s[/tex]
Ticket equation:
[tex]1500=a+s[/tex]
Now just solve the system of equations for s:
[tex]15480-12a=6s\\ \frac{15480}{6} - \frac{12a}{6} =s\\ 2580-2a=s\\ 1500=a+s\\ 1500=a+(2580-2a)\\ 1500=-a+2580\\ 1500-2580=-a\\ -1080=-a\\ 1080=a\\ \\ 1500=a+s\\ 1500=1080+s 420=s[/tex]
420 Students attended
