How do you earn farm cash on FarmVille?

I am currently at level 23 with Facebook's Farmville (FV). I have been able to "earn" Farmville cash or dollars in several ways, without buying them: increase in ones level, purchases of high ticket items, gaining experience points (xp), moving up in the ribbon status, repetitive plantings (related to xp's), and by taking advantage of the "free" offers when you click on the "Need more " button link and maneuvering to the bottom portion (sometimes these are not really free and often the promised dollars never materialize, but I have received well over 20 FV dollars from this activity). his all takes time and patience, but if you continually plod along with the game the FV dollars will eventually appear. Yes, it is a slooooow process. I believe, but have not yet been able to verify, that there is an algorithm (mathematical equation) running in the background of each account that keeps track of the activity. When certain predetermined point levels are reached for the various game activities (that are different values based on complexity) the Farmville cash is awarded. Nothing scientific here, just my observations on the game so far.