Answer
It is not important.
Work Step by Step
Units on the Kelvin scale and on the Celsius scale have the same size increments, i.e., a kelvin is the same size as a Celsius degree (as stated on page 286). Thus, a temperature difference expressed in kelvins or in Celsius degrees is the same.
Newton’s law of cooling deals with temperature differences, so one does not need to convert between the 2 scales.