Remaining part = \( \frac{3}{4} \) of the race = 12 km.
Full race distance = 12 ÷ 3 × 4 = 16 km.
First \( \frac{1}{4} \) = 16 − 12 = 4 km.
New speed for remaining part:
• 25% faster = 8 × 1.25 = 10 km/h
Time for first 4 km at 8 km/h:
• 4 ÷ 8 = 0.5 h = 30 min
Time for remaining 12 km at 10 km/h:
• 12 ÷ 10 = 1.2 h = 72 min
Total time = 0.5 + 1.2 = 1.7 h = 1 h 42 min.
Final Answer: 1 h 42 min