Final answer:
The child's speed is 0.5 m/s.
Step-by-step explanation:
To find the speed in m/s, we need to convert the distance and time given into the appropriate units. The child rides his bicycle 90 meters in 3 minutes. To convert minutes to seconds, we multiply by 60, so the time is 3 minutes x 60 seconds/minute = 180 seconds. Therefore, the speed is distance/time = 90 meters / 180 seconds = 0.5 m/s.