The formula relatinf wattage and monthly cost is:
For this case, the wattage W is 1500 w.
The time of usage is t = 0.25h per day. Equivalent to 30*0.25 = 7.5hr/month
The cost of electricity per kilowatt-hour is c = 0.15$/kWh.
With this infomration we can calculate the monthly cost to run the hair dryer, by rearranging the equation and solving for C:
The cost per month to run the hairdryer is approximately $1.69