roberto owns a bicycle shop where he sells and repairs bicycles. his revenue is $400,000 per year. his shop is in a building that he owns and could rent for $20,000 per year. he has an assistant to whom he pays a $30,000 salary each year. he paid $100,000 to purchase the inventory of bicycles he sells. he pays a total of $50,000 in taxes, insurance, and utilities each year. in order to operate his shop, roberto gave up his job as a cpa, where he earned $100,000 per year. roberto's accounting profit is: