The sole proprietor of the "Books and Children" bookstore receives all accounting profits earned by her firm and a $28,000-a-year salary she pays herself. She has a standing salary offer of $35,000 a year if she agrees to work for a large corporation. If she had invested her capital outside her own company, she estimates that would have returned $22,000 a year. Last year, her accounting profit was $50,000. a. Calculate her implicit cost. b. Calculate her economic profit