question: Linus works for a trading company. He buys a mobile device for $20 and sells it for twice the amount of the original price. If he bought 2 devices last Monday and 4 devices last Tuesday, how much profit was he able to earn after selling all the mobile devices he bought last Monday and Tuesday?
answer: The total cost for the devices he bought on Monday is 2*20= <<2*20=40>>40
  The total cost for the devices he bought on Tuesday is 4*20 = <<4*20=80>>80
  The total cost of these devices is 80+40= <<80+40=120>>120
  Linus sold each mobile device he bought for $20 x 2 = $<<20*2=40>>40.
  So, he earned $40 x 2 = $<<40*2=80>>80 for the two devices he bought last Monday.
  And he earned $40 x 4 = $<<40*4=160>>160 for the 4 devices he bought last Tuesday.
  The total amount of sales he made were worth 160+80 =<<160+80=240>>240
  Linus earned 240-120 =$<<240-120=120>>120
  #### 120