If you are a high school student taking AP Computer Science A (or any introductory Java course), you have likely encountered a moment of digital dread. You are clicking through the "Methods" unit, feeling confident about loops and arrays, and then you hit it: Unit 9: Inheritance. Lesson 6: Polymorphism. Problem 7: Cars.

Today, we aren't just going to give you the code. We are going to reverse-engineer why this problem breaks so many brains, and how to actually understand it. Most students looking for "9.6.7 answers" are stuck because they are trying to treat Java like LEGOs—just snapping pieces together. The problem requires Polymorphism and Inheritance , two concepts that don't make sense until your code actually fails.

If you copy the raw code from a forum, you will likely fail the because of variable naming mismatches. The autograder checks for specific method signatures (e.g., getManufacturerInfo() vs getInfo() ). One typo, and you get a 0. The Ethical Walkthrough (How to actually solve 9.6.7) Let's build the solution conceptually so you don't need to cheat.

Stuck on a specific error? Drop the compiler error message in the comments—chances are, you forgot to call super() in your subclass constructor.