The washing machine is used 4 hours per week. One month contains 4 weeks, so the total time the washing machine is used in one month is
t= 4 weeks x 4 h/week=16 h
The total energy consumed in 4 weeks is the power multiplied by the time:
[tex]E=Pt = (750 W)(16 h)=12000 Wh=12 kWh[/tex]
The cost of the washing machine is 0.15 $ per each kWh of energy, so the total cost is
12 kWh x 0.15 $/kWh = 1.8 $
