If the paragraph were properly punctuated, it would have 5 sentences ending with periods. Here is one way to punctuate the paragraph:
"Huckleberry Finn was an excellent book. It told of a raft journey down the Mississippi. The book has been enjoyed by children and adults. I like to read it once a year. Maybe we all have that desire to be free; you can get away from it all when you read about Huck."
Thus, the answer is 5.