Answer: $100
Explanation:
From the information, on a Friday night, you have the choice to either go to a Katy Perry concert or a Lady Gaga concert. You won a free ticket to see Katy Perry but you would pay as much as $180 to see Lady Gaga perform, even thought the tickets to her show cost $100.
This illustrates that the person must be willing to pay at least $100 to see Katy Perry. Since the person wa.willing to pay $180 for Lady Gaga even when the tickets were$100, then you should be able to pay at least $100 to see Perry