That question gave me a headache when I first encountered it a long time ago. But @DumbHollywoodActor nailed it. Follow J.Y's principle with negating necessary and negating sufficient when indicators kick in, and you should be fine.
The same subject will not always be as obvious as in the first sentence. For the second one, you could say that the "way" or " a route" would be the subject addressed by both the sufficient and necessary conditions.