How much energy is transferred by five 60 watt bulb in 20 minutes

(5 bulbs)·(60 watts/bulb)·(20 minutes)·(1 joule per sec/watt)·(60 sec/minute)

=  (5·60·20·1·60)  (bulb·watt·minute·joule per sec·sec) / (bulb·watt·minute)

=        360,000 joules


Another way:

Five 60-watt bulbs  =  300 watts  =  0.3 kilowatt

20 minutes  =  1/3 hour

              (0.3 kilowatt) · (1/3 hour)  =  0.1 kilowatt-hour