Answer: Opportunity cost of Dr. Richard's wednesday afternoon golf outing is $580.
Explanation: Opportunity cost as the name suggests is the cost of the lost alternative. In this case, when Dr. Richard chooses to play golf instead of going for his Dr.'s practice he is forgoing the earning which he could have earned from his practice.
As given in the problem, he could have earned $100 per hour from going to his practice. Since, playing golf takes 5 hours it means that he is sacrificing his 5 hours income from the practice. So, his opportunity cost should be $500. Moreover, he also spends $20 for lunch and $60 for his golf practice which he would not have spent in case if he didn't play golf.
Total Opportunity cost is $580