Detailed Solution: GIVEN: By cycle: Distance = 15 km Speed = 5 km/hr By bike: Distance = 30 km Speed = 15 km/hr FORMULA USED: Speed = Distance / Time CALCULATION: ⇒ Distance covered by cycle @ 5 km/hr = 15 km ⇒ Time taken in this journey = 15/5 = 3 hours ⇒ Distance covered by bike @ 15 km/hr = 30 km ⇒ Time taken in this journey = 30/15 = 2 hours ⇒ Total time = 5 hours ⇒ Total distance = 45 km ⇒ Average speed = 45/5 = 9 km/hr