Why or why not was it the right decision for Ponyboy to run away with Johnny Cade? Please explain.

This question asks you to state your opinion and then to support your opinion with evidence from the novel. Here are some ways to begin to formulate your ideas.
First of all, think to yourself if you would have advised Ponyboy to run away with Johnny had he come to you for advice. What questions might you have asked Ponyboy and how might he have answered? For example, if you asked Ponyboy why he wants to go with Johnny, he might say he doesn't want Johnny to go on his own, or he is scared he will get in trouble with the police. How do you feel about these responses? If you understand Ponyboy's motivation for wanting to accompany Johnny while he goes on the run, then perhaps you would support his decision. However, if you don't agree with Ponyboy, you might advise him not to go.
Once you are clear on where you stand on these kinds of issues, you will be in a better position to answer the question. If you do agree that Ponyboy should have gone with Johnny, you might discuss the terms and conditions of their friendship and the protective feelings Ponyboy might have for Johnny. As well, you might discuss the position of Greasers in society as a way to justify their avoidance of the police. On the other hand, if you disagree with Ponyboy's decision, you might back up your ideas with an argument that involves the emotional impact of Ponyboy's disappearance on others, like his brothers, or the legal impact of evading the law.