you buy only apples and bananas. Your budget is such that you can purchase 3 apples and 4 bananas or 9 apples and 2 bananas. Write down the equation for the budget line with bananas on the y-axis. Is that equation unique

Answer 1

Of course this is not unique. One could buy all apples, or all bananas. Notice that each banana is worth three apples, so one could buy 5 bananas, or 15 apples.