The energy flux from the sun has a peak value of around 1500 W/m2, and solar cells are around
15% efficient. Estimate the area needed to satisfy US energy needs using solar cells, using the
estimates that there are about 350 million people in the US and that we use an average of 90
kW/person. Also assume that there are about 6 hours of "peak" sunlight per day. Answer in square
kilometers (do not put units in your answer, however).