question: 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?
answer: Ada's weekly electric consumption before adding the new device is 12 x 7 = <<12*7=84>>84.
  So, her weekly electric bill is 84 x $1.50 = $<<84*1.5=126>>126.
  Ada's daily electric consumption after adding the new device is 12 + 2 = <<12+2=14>>14.
  So her weekly electric consumption after adding the new device is 14 x 7= <<14*7=98>>98 kilowatts per hour.
  Ada's new electric bill per week will be 98 x $1.50 = $<<98*1.5=147>>147
  Therefore, the difference between the bill before and after she adds the new device is $147 - $126 = $<<147-126=21>>21.
  #### 21