Hello!
The first thing you want to do is add 13+5 which gives you 18. SO then you see how many times 18 goes into 360. Which gives you 20. So then you multiply 20 by 5 (because there are 5 business seats for every 13 and 18 went into 360 20 times, which gives you 100 business seats. Then you subtract 100 from 360 to see how many economy seats are left which gives you 260 economy seats. So there are 100 business seats and 260 economy seats.
I hope this helped!
I am, yours most sincerely,
SuperHelperThingy