The first requirement is to look at all the vital information’s given in the question. Based on those information’s the answer to the question can be easily reached.
Distance that needs to be covered for the race = 38.4 kilometer
Time required to complete the race = 4.5 hours
Then
Average speed = Distance/Time
= 38.4/4.5 km/hour
= 8.53 km/hr
So the average speed would be 8.53 Km/hr. I hope the answer to the question is what you were looking for and the procedure is clear to you.