Normally, promotions only offer two Farm Cash, so this is really like two promotions in one. To complete it, you'll need to look for the free Farm Cash bubble on the right side menu of the FarmVille gameplay area. The promotion itself asks you two poll questions and then allows you to instantly return back to your farm where your Farm Cash total should automatically update, reflecting your participation. If not, a simple refresh of your game should do the trick to set things right.
Unfortunately, this looks to be the only Farm Cash promotion available as of this writing, but we'll make sure to update this space if and when further promotions launch in the game. In the meantime, feel free to treat yourself to a few building materials or a cheap decoration in the game's store with your prize "money!"
Do you have this promotion available to you in your game? What will you do with the four Farm Cash you've earned? Sound off in the comments.