To find the average speed of the runners in the relay, we first need to calculate the total distance and the total time taken by all four runners.
The total distance for the relay is 400 meters (100 meters for each of the 4 runners).
Now, let's calculate the total time taken by the runners:
- First runner: 15 seconds
- Second runner: 17 seconds
- Third runner: 15 seconds
- Fourth runner: 13 seconds
Total time = 15 + 17 + 15 + 13 = 60 seconds
Now we can find the average speed using the formula: \[ \text{Average Speed} = \frac{\text{Total Distance}}{\text{Total Time}} \] \[ \text{Average Speed} = \frac{400 \text{ m}}{60 \text{ s}} = \frac{400}{60} \approx 6.67 \text{ m/s} \]
Thus, the average speed of the runners is approximately 6.7 m/s.
Therefore, the correct response is: 6.7 m/s.