What is the right course of action?

You answered correctly. In this situation, you see a yield (give way) sign, which means you must yield to all cross traffic. The blue truck is coming from your left and has no yield sign, so you must let it pass first. The tractor is turning left across your path, and since you are facing a yield sign and the tractor is already on the priority road, you must also let the tractor turn. The blue truck does not need to allow you to go first, because it is on the priority road. Remember: At a yield sign, always let all vehicles on the priority road go first, regardless of their direction. This will help you answer similar questions in the future.