1)
Here it says to answer a Kesil. The previous verse said not to answer him!
1.
Rashi #1: If he comes to entice you to evil, inform him of his folly.
2.
Rashi #2: Do not answer him about a matter that will equate you to him. Answer him in a matter that if you do not answer him, he will be a Chacham in his eyes.
3.
Malbim: Answer him with light matters - the primary intent is to show that he is a Kesil. Do not answer him with sharp matters to show your Chachmah.
2)
Why will he be a Chacham in his eyes?
1.
Malbim: He will think that you did not find an answer for him.
