Billy wants tickets huh okay.....
Alright so first off what information do we have?
We know that 4 adult tickets are 15 Euros each
2 child tickets are 10 Euros each
Ok simple calculations here
4*15 = 60
2*10 = 20
Total is 80 Euros charge
10% booking fee
so 10% of 80 is 8 (Add this onto the total bill) = 88
3% of 88 is (well 1% is 0.88 3% is 0.88 * 3 = 2.64)
Total bill now is 90.64 (Might aswell add taxes now poor billy spending a 100)
By the way your answer is 90.64