[
  "The remaining 3/4 = 12 km, so full race = 16 km and first 1/4 = 4 km.",
  "New speed = 8 km/h + 25% = 8 x 1.25 = 10 km/h.",
  "Total time = 4/8 + 12/10 = 0.5 + 1.2 = 1.7 h = 1 h 42 min."
]