He could have wrote -2.5 or -3.
If x is the childrens ticket

so that means that the adults ticket is
Idk, I think 8.5 bc 12 is half of 24, and half of 17 is 8.5. I tried lol
The price would be 2.60*2.5=$6.50
Just multiply the price cause it’s by the pound and multiply it by how many pounds