What should you do if you see a green lighted buoy with the number 3.?

If you see a green lighted buoy marked with the number 3, it indicates a navigational aid for vessels. Generally, green buoys are used to mark the port side of a channel when entering from the sea, meaning you should keep the buoy on your left side. Always ensure to follow local navigation rules and guidelines for safe passage. If you're uncertain, consult a nautical chart or navigational resources for further information.