Answer:
20 m/hr
Explanation:
distance / rate = time
24 miles / 9 miles/hr = 2 2/3 hr
(24 + 20 miles) / 12 miles/hr = 3 2/3 hr
3 2/3 - 2 2/3 = 1 hour to ride the next 20 miles means 20 m/hr
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