How do you answer this?

I hope you have a statistics book - you'll need it. You'll need a z-score table (usually found at the back of the book) and you'll need to find the formulas for determining probabilities from proportions of areas under a probability function (which in school is usually the normal curve). If you have trouble making sense of that last sentence - just find similar problems in a statistics book. Once again, I hope you have a book...or maybe a statistician floating around on yahoo! answers.