I didn’t understand the instruction of this challenge on codewars platform. I didn’t understand how to calculate the system B .
So I need explanation about how to calculate system B If John goes to the cinema 3 times or 5 times?

system B starts it has a price of 500 at the beginning. And then each ticket costs 15*0.9^{n} where n is the number of the ticket (first ticket costs 15*0.9^{1}, second ticket 15*0.9^{2} and so on)