The formula relatinf wattage and monthly cost is:
[tex]W=\frac{1000C}{tc}[/tex]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:
[tex]C=\frac{Wtc}{1000}[/tex][tex]\begin{gathered} C=\frac{(1500)\cdot(7.5)\cdot(0.15)}{1000} \\ C\approx1.69 \end{gathered}[/tex]The cost per month to run the hairdryer is approximately $1.69