2. Find a piece of formal writing and a piece of informal writing, compare the two and list [.....]

An example of a piece of Formal Writing:

"This is to inform you that your book has been rejected by our publishing company as it was not up to the required standard. In case you would like us to reconsider it, we would suggest that you go over it and make some necessary changes." (http://ezinearticles.com/?The-Difference-Between-Formal-and-Informal-Writing&id=594208)

And an example of Informal Writing:

"You know that book I wrote? Well, the publishing company rejected it. They thought it was awful. But hey, I did the best I could, and I think it was great. I'm not gonna redo it the way they said I should." (http://ezinearticles.com/?The-Difference-Between-Formal-and-Informal-Writing&id=594208)

The main differences between these two texts are the choice of words and sentence structure. The person who wrote the text in the first example chose to not put emphasis on the company that rejected the book, instead they put the emphasis on the book that was rejected (by the company, which functions as the agent here) thus making the sentence passive. However in the second example, which could be a conversation between two friends, the emphasis is put on the company that rejected the book thus making the sentence active.
Going back to the sentences we can clearly see that the formal example is making use of longer, more complex, sentences whereas the informal is using short and simple sentences which is acceptable in normal everyday language.