What is the cost of operating a 3.00-w electric clock for a year if the cost of electricity is $0.0900 per kw · h ?

We must take into account the following change of units:
 
 Applying the change of units we have that the electric consumption for 1 year is given by:
 
 Then, the total cost is given by:
 
 
 the cost of operating a 3.00-w electric clock for a year is:
 $ 2.3652