一道题目不会做，想请教一下诸位。He only buy apple and banana, He prefers more apples to less, He is tired of bananas. If he consumes fewer than 17 apples, he think one banana is perfect substitutes to one apple. But you would have to pay him one apple for each banana beyond 17 that he consumes. The Indifference curve that passes through the consumption bundle with 25 apples and 26 bananas. IC also passes through N apples and 11 bananas.
where, N equals to ?

麻烦好心人回答一下了，如果没人回答以后就不来问了。