Electricity from the local power company costs 5.28 cents/kwh. a homeowner wishes to pay a maximum of 30 cents per month for the electricity to power a 120-w stereo system. for how many hours per month could the stereo system be used?

The maximum cost allowed in one month is 30 cents. Since electricity costs 5.28 cents/kWh, the maximum energy that can be used is


The stereo system uses a power of P=120 W. Since the power is the energy per unit of time:

the stereo system can be used for a number of hours equal to:

Gas will most likely  fill the container