David opened a candy store. He rented a building for $30,000 a year. During the first year of operation, He paid $40,000 to his employees, $10,000 for utilities, and $20,000 for goods he bought from other firms. His total revenue was $135,000. David's best alternative to running this candy store is to work for Target as a sales associate for $15,000 a year. What is David's economic profit? Show your complete steps/calculation