Suppose you have a choice to go to a Katy Perry concert or a Lady Gaga concert on Friday night. You won a free ticket to see Katy Perry. You would pay as much as $150.00 to see Lady Gaga perform, but a ticket to her show costs $100.00. Suppose a friend offers you $65.00 for the Katy Perry ticket. The opportunity cost of going to the Katy Perry concert is $ .