In a murder investigation the temperature of the corpse was

In a murder investigation, the temperature of the corpse was 33 degree C at 1:30pm and 25 degree C 2 hours later. Normal body temperature is 37 degree C and the surrounding temperature was 7 degree C. How long (in hours) before 1:30pm did the murder take place?

The murder time is 10:45 I.e. three hours forty five minute