Suppose 60 percent of the people in a country support a law.

Suppose 60 percent of the people in a country support a law. A group of N people participate in a referendum about the law, and the law is passed if at lest half of the participants vote in favor of the law. If the opinions are independent, what is the N for which the law is passed with probability 99.9%? 

Please explain step by step in detail.