A local flower store determines its average customer's demand per year is Q=10-4P, and knows the marginal cost of the good it sells is $1.0. What is the amount that the flower store should charge as a fixed fee if it engages in optimal two-part pricing?

a. $1

b. $2.5

c. $4.5

d. $6

If you could show how you got there it would be greatly appreciated.