Read the following and answer Questions 1a and 1b.

Andy has just been offered an extra evening shift for 3 hours at Coles. He would earn $100 if he takes it. However, he already plans to go with his mates and catch the latest Avengers movie: 'Avengers: the Game does not End yet'. The movie ticket costs $20.

Question 1a. Explain what opportunity cost means.

Question 1b. Consider the example of Andy. What do you think is the total opportunity cost for Andy if he decides to go to the movies?

Please, answer these above questions.