Barney decides to quit his job as a corporate accountant, which pays $13,000 a month, and goes into business for himself as a certified public accountant. He runs his business from his converted garage apartment, which he could rent out for $310 a month if he wasn't using it as a home office. He must purchase office supplies worth $75 a month, and his monthly electricity bill has increased by $50 now that he is working out of his home office. After six months of working from home, Barney has earned an average of $18,000 per month. Instructions: Enter your answers as a whole number. a. What are Barney's monthly explicit costs? b. What are Barney's monthly implicit costs? c. What are Barney's monthly economic costs?