To find the distance covered when walking at an average speed of 4 m/s for 5 seconds, you can use the formula:
\[
\text{Distance} = \text{Speed} \times \text{Time}
\]
Given:
- Speed = 4 m/s
- Time = 5 s
Calculating the distance:
\[
\text{Distance} = 4 \, \text{m/s} \times 5 \, \text{s} = 20 \, \text{m}
\]
So, the distance covered in 5 seconds is 20 meters.
The correct answer is **d. 20 m**.