Internal temperature of a body is 80.4* and there are no factors
influencing algor mortis. How long has the person been dead?

Patient may appear to be dead. 24–26 °C (75.2–78.8 °F) or less – Death usually occurs due to irregular heart beat or respiratory arrest; however, some patients have been known to survive with body temperatures as low as 14.2 °C (57.6 °F).

Explanation:

Algor mortis is the second stage of death.

Glaister equation is used to determine the time elapsed  since death which is

Therefore, it has been 12 hours since the person is dead.

if you know your abc's you should be able to get your answer or just use google