According to Zipf's Law, the number of cities N with a population greater than S is inversely proportional to S. In 2008, there were 51 U.S. cities with a population greater than 300,000. Estimate (a) the number of U.S. cities with a population between 300,000 and 400,000; (b) between 250,000 and 550,000. a. According to Zipf's Law, the number of U. S. cities with a population between 300,000 and 400,000 is approximately . (Round to the nearest whole number as needed.)