[
  "Break 8000 into factors: 8000 = 1000 x 8. Then 1680 / 8000 = 1680 / 1000 / 8.",
  "1680 / 1000 = 1.68. Then 1.68 / 8 = 0.21.",
  "Answer: first blank = 1000, second blank = 1.68, third blank = 8, fourth blank = 0.21."
]