For this problem we have two trajectories given the first one with 25 km and 5 hours and a second one exactly the same.
From the definition of average speed we have the following formula:

Where distance represent the total distance travelled and time the total time ellapsed. From the problem we know that: distance = 25+25 km= 50 km and time= 5+5 hr = 10 hr. so then replacing into the formula given we got:
![V_{\text{avg}}=\frac{50\operatorname{km}}{10hr}=5(km)/(hr)]()
So then we can conclude that the average speed is 5 Km/hr