Ahair curling iron uses 13 watts of power. how long must it operate to do 1,040 joules of work?

Knowing the solution to the 4-watt night light, you ought to be able to do this one on your own.  But 5 points is 5 points, so here we go:

1 watt = 1 joule/second .

                            (1,040 joule) / (13 joule/second)

                        =    (1,040 / 13) (second)

                        =       80 seconds .  

Power of Watt = Energy in Joules / Time period in seconds

13 watts = 1040 joules / time in seconds
time in seconds = 1040 joules / 13 watts
time in seconds = 80 seconds

It must operate for 80 seconds to do 1,040 joules of work.