[
  "Find the base area: 40 cm x 25 cm = 1000 cm2.",
  "Initial water height: 6000 cm3 / 1000 cm2 = 6 cm.",
  "Cubic tank holds 1000 cm3. Remaining: 6000 - 1000 = 5000 cm3. Height = 5000/1000 = 5 cm."
]