The average American uses electrical energy at the rate of about 1.5 kilowatts . Solar energy reaches Earth's surface at an average rate of about 300 watts on every square meter.What fraction of the United States' land area would have to be covered with solar cells to provide all of our electrical energy? Assume the cells are 20% efficient at converting sunlight to electricity. this is from the first chapter on units. Don't I need the us's size and population for this? Can anyone give me hints on how to get the answer?