[
  "Draw a bar model: Bag A = 5 units, Bag B = 1 unit, Bag C = 4 units. Total units = 5 + 1 + 4 = 10.",
  "10 units = 20 kg, so 1 unit = 20 / 10 = 2 kg. Bag B = 2 kg, Bag C = 4 x 2 = 8 kg.",
  "Difference: 8 - 2 = 6. Answer: 6 kg (option B)."
]