Final answer:
The appropriate altitude for an aircraft under VFR in level cruising flight on a heading 090 degrees would be 4,500 feet.
Step-by-step explanation:
For VFR operations above 3,000 feet AGL and below 18,000 feet MSL, there are rules for altitude selection based on magnetic course. The appropriate altitude for an aircraft under VFR in level cruising flight on a heading 090 degrees would be 4,500 feet. This is because the general rule is to fly at odd-thousands plus 500 feet when on an eastbound magnetic course.