"re-type the celsius_to_kelvin function. change the name to kelvin_to_celsius, and modify the function accordingly."

You didn't include the original function, but the new function will contain something like:

function kelvin_to_celsius(k)

{

  return k - 273.15;

}

Depending of course on your programming language.

The outcome for negative Kelvin is undefined, you could test for that.

answer inspecting packets in isolation from their context;