Question: I'm completely lost with this math problem: Ada's daily electric consumption is 12 kilowatts per hour. She is planning to add a device that will consume 2 kilowatts per hour a day. If a kilowatt per hour is $1.50, how much is the difference between Ada's weekly electric bill before and after she adds the new device?
Can you give me a hand?
Answer: 
Ada's weekly electric consumption before adding the new device is 12 x 7 = 84.
So, her weekly electric bill is 84 x $1.50 = $126.
Ada's daily electric consumption after adding the new device is 12 + 2 = 14.
So her weekly electric consumption after adding the new device is 14 x 7= 98 kilowatts per hour.
Ada's new electric bill per week will be 98 x $1.50 = $147
Therefore, the difference between the bill before and after she adds the new device is $147 - $126 = $21.