The sole proprietor of the Milwaukee Machine Company generates an annual accounting profit of $78,000. She has a standing salary offer of $35,000 a year to work for a large corporation. If she had invested her capital outside her own company, she estimates it would have returned $22,000 this year. What is the sole proprietor's economic profit? A) $0 B) $13,000 C) $21,000 D) $43,000