let us repersent the number of student tickets, then 's + 20' is repersenting the number of adult tickets.
The equation for the total tickets can be experssed as the following:
4.00 * s + 8.00 * ( s + 20 ) = 880.00
solving for 's=60', there were 60 student tickets.
60 + 20 = 80
there were 80 adult tickets.
Hope helps!-Aparri