Krista sets up a business selling coffee from a coffee cart. She earns $12,000 in revenue a month. She incurs costs of $3000 per month in supplies (coffee cups, creamer, sugar, pastries, napkins, and so on). She used to earn $3500 per month as a barista. The coffee cart is very specialized and has no other uses. What is Krista's implicit cost of capital per month?