Bob consumes only apples and bananas. He always prefers more apples to fewer, but he gets tired of bananas. If he consumes fewer than 29 bananas per week, he thinks that 1 banana is a perfect substitute for 1 apple. But you would have to pay him 1 apple for each banana beyond 29 that he consumes. His indifference curve that contains the consumption bundle with 30 apples and 39 bananas also contains the bundle with 21 bananas and how many apples?

Please answer using graphs and all the details.