(a) As of 2021, Earth's human population is roughly 7.9 x 109, and its total land area excluding the polar caps is roughly 5 x 107 square miles. If the human population were distributed uniformly over all available land, approximately how many persons would be found per square mile? (b) At the speed of light, which is 3 x 103 meters per second, how many seconds does it take for the sun's light to travel the 1.5 x 1011 meters to Earth