Final answer:
To keep the monthly electricity bill below $20 when the cost structure is $8 fixed plus $0.03 per kWh, a maximum of 400 kWh can be used. This is found by subtracting the fixed cost from the maximum bill allowable and then dividing by the variable cost per kWh.
Step-by-step explanation:
To determine the amount of electricity use that will keep the monthly bill below $20 when electricity costs $8 a month plus $0.03 per kilowatt-hour, we can set up an inequality to solve for the maximum number of kilowatt-hours. The total monthly bill (B) is the sum of the fixed monthly charge ($8) and the variable charge based on electricity usage ($0.03 per kWh). The inequality can be represented as:
B = $8 + ($0.03 \times kWh) < $20
To find the number of kWh that will keep the bill under $20, we subtract the fixed charge from the maximum total charge and then divide by the cost per kWh:
($20 - $8) / $0.03 per kWh = 400 kWh
Therefore, to keep the electricity bill under $20, one would have to use less than or equal to 400 kilowatt-hours of electricity. The correct answer is A) 400 kilowatt hours.