Finding where the Throttle cable is and is it expensive to replace

What is your question?

I just bought this used car. As I was driving it jumps into neutral ( maybe hit a bump), did this 3 times within an hour.. but it tends to not want to go into park or while in neutral I can still push gas pedal and it goes. I want to know IF this is the problem. A man looked at it and said the cable was stretched a bit.