1) Look up the wattage of one of your lightbulbs in your home. What is the resistance of that light bulb if it was designed to be on a 120-V circuit?
2) An energy efficient space heater draws 12.5 amps of current across a 120-V circuit. What is the power of that energy efficient space heater?
3) Look up your local cost per kilowatt-hour and determine how much it would cost to run that energy efficient space heater for 3 hours.