Let's imagine all the tickets were for children.
The fees collected would've been 342 x 1.25 = $427.5
That is 1337 - 427.5 = $909.5 less than the actual fees.
Everytime we switch 1 children ticket to an adult ticket, the gap goes down 6.60 - 1.25 = 5.35
For example, if 341 tickets were children tickets, and 1 is adult, the gap go from 909.5 to 904.15.
We do this until the gap becomes 0... So, there are 909.5 : 5.35 = 170 adult tickets
And there are 342 - 170 = 172 children tickets
Recheck : 172 x 1.25 + 170 x 6.6 = 215 + 1122 = 1337.
