Joan can only choose to do one of three options with her spare time. First, she could go to see a movie (which costs $15 for a ticket) but Joan values at $30. Second, she could go to a friends party (which costs nothing) but Joan values at $20. Finally, she could take an extra shift at work where she will earn benefits of $30, but she has to pay $5 for public transport to get there.

What is Joan's opportunity cost of going to the movie? (In this case, you should think of the opportunity cost as including any direct costs incurred, as well as the value of the next-best alternative).

Group of answer choices

a) $15

b) $25

c) $40

d) $60