Hello,
Imagine Algebra does not exist .
Let's suppose all tickets are children's tickets
The sum should be 5$*375=1875$
Not enough, we must have $2153: 2153-1875=278 ($) must be found.
Let's replace a children ticket with an adult one,
we get one dollar more.
We must thus exchange 278 tickets
There are 278 adult tickets and 375-278=97 children tickets
Proof: 278*6+97*5=2153