Ask lots of questions and if you have assumptions, make it known. There is no right answer but there are answers more right than some. This question tests a wide range of skills including: 1. Coding Best Practices 2. Writing Clean Code 3. Troubleshooting & Maintenance 4. Analysis 5. OOD (Object Oriented Design) 6. Requirements Gathering 7. Design for Testing 7. Etcetera... Just be prepared to design and re-implement based on your prior knowledge.