Sara's income is $12 a week. The price of popcorn is $3 per bag, and the price of a smoothie is $3 per cup.

1. Calculate Sara's real income in terms of smoothies. Calculate her real income in terms of popcorn. Explain (4 marks)
2. What is the relative price of smoothies in terms of popcorn? What is the opportunity cost of a smoothie? Explain (4 marks)
3. Determine the equation for Sara's budget line. Explain (2 marks)