Sam is deciding whether to take a one-year full-time singing course after completing a part-time introductory vocal course in a music academy. If he chooses not to study, he can work as a music teacher. Some of his costs are listed below. I. A one-year tuition fee of $100,000 for the singing course II. An annual rent for the coming year of $60,000 on the flat which has been living for the last 10 years III. The annual income of $180,000 for being the music teacher IV. The course fee of $20,000 for the introductory vocal course a. Explain which of the above costs should be regarded as the cost of studying the singing course. (4 marks) b. Use the concept of cost to explain why more people choose to study during economic recession.