To find the time it takes for the zebras to walk 500 meters at a rate of 2.1 m/s, we can use the formula:
\[ \text{Time} = \frac{\text{Distance}}{\text{Speed}} \]
Here, the distance is 500 meters and the speed is 2.1 m/s.
Plugging in the values:
\[ \text{Time} = \frac{500 \text{ meters}}{2.1 \text{ m/s}} \approx 238.1 \text{ seconds} \]
Thus, it will take the zebras approximately 238.1 seconds to reach the Sunglasses R Us store.