Dead Whale

In Autumn $2011$ a sperm whale stranded at a beach on the island Pellworm. Even though the whale had been dead for some days already, the measured body temperature of the whale on $21$ November was $20$ $°C$ . Three days later it had sunk to $15$ $°C$ .

The cooling of an unheated body in air can be modelled by a temperature curve as shown in the graph.

Using the given information, make an estimate of the time of death of the sperm whale. Assume that the outside temperature remained constant at around $0 °C$ during the cooling and that the body temperature at the time of death was $37 °C$ .