An electric heating element is connected to a 110 v circuit and a current of 3.2 a is flowing through the element. how much energy is used up during a period of 5 hours by the element

Power (rate of using energy) = (voltage) x (current)

Power of this heating element = (120 V) x (3.2 A) = 384 watts

The easy way:

     384 watts = 0.384 kilowatt

     (0.384 kilowatt) x (5 hours) = 1.92 kilowatt-hour

Another way:
     
                            384 watts = 384 joules per second .

        (384 joule/sec) x (3600 sec/hour) x (5 hours)  

=      (384 x 3600 x 5) (joules)  =  6,912,000 joules.