[
  "Multiply the change factors: 1.20 (length +20%) x 0.90 (width -10%) = 1.08 before height change.",
  "Overall volume factor is 0.96 (4% decrease). So 1.08 x (1 + r/100) = 0.96.",
  "Solve: 1 + r/100 = 0.96 / 1.08 = 0.8889..., so r/100 = -0.1111..., r = -11.11%."
]