The fingers on your hand are approximately 0.5 cm apart. ignoring atmospheric blurring, what size mirror would a spy satellite have to have in order to tell how many fingers you are holding up at it using visible light (wavelength = 500 nm) at an altitude of 200 km?

An electric power distributor charges residential customers $0.10 per kilowatt-hour (kwh). the company advertises that "green power" is available in 150 kwh blocks for an additional $4 per month. (green power is generated from solar, wind power, and methane sources.) if a certain customer uses an average of 391 kwh per month and commits to one monthly 150 kwh block of green power, what is her annual power bill