Running time = 120 min = 2 h, split equally between two speeds: 1 h each.<br><br>&bull; Distance at 12 km/h = 12 × 1 = 12 km.<br>&bull; Distance at 18 km/h = 18 × 1 = 18 km.<br>&bull; Total running distance = 12 + 18 = 30 km.<br><br>Total time (including 60 min rest) = 120 + 60 = 180 min = 3 h.<br>Overall average speed = 30 ÷ 3 = 10 km/h.<br><br>Final Answer: 10 km/h