You should now be able to work out how much it costs to run an electical appliance as long as you know its power rating, the time you use it for, and the cost of electrcity.
Energy = power × time can be used as long as power is in kW and time in hours. The formula becomes:
Units used (kWh) = power (kW) × time (h)
e.g. A 2·5 kW kettle is used for 2 hours a week. Units cost £0·08 each.