The speed of sound at any given temperature is given by:
![v_s=331.3\sqrt[]{1+(T)/(273.15)}](https://img.qammunity.org/2023/formulas/physics/college/3iktn9twuabbdli3j0u2mqg7syldpmspg0.png)
We know that in this case the temperature is 20°, then the speed of sound is:
![v_s=331.3\sqrt[]{1+(20)/(273.15)}=343.21](https://img.qammunity.org/2023/formulas/physics/college/ioezu6r8nx60zkm1vwrytuo46v9wvjz5yx.png)
Now, the distance is given by:

Plugging the speed we found for the sound and the time it takes Karen to hear the thunderclap we have:

Therefore, the lighting stroke 1029.64 m away