If you can complete this time consuming task (which relies more on luck and repetition than skill), you'll receive 10 free energy and five free Zoning Permits in CityVille.
This CityVille promotion is similar to that in FarmVille, both in the task required to earn your prize and in the disappointing prizes actually being offered. For such a time-consuming, and even difficult promotion to complete, it would have been great to receive a better prize in the end.
Either way, this promotion will likely only be available to complete for a limited period of time, so if you've yet to complete the 10 full Zynga Slingo cards, make sure to do so sooner, rather than later in order to earn your free (albeit disappointing) prizes.
What do you think of this second cross-promotion in CityVille? Sound off in the comments.