Please see the attached file.

Theory
Newton's Law of Cooling describes the cooling of a warmer object to the cooler temperature of the environment. Specifically we write this law as,
T (t) = Te + (T0 − Te ) e - kt,
where T (t) is the temperature of the object at time t, Te is the constant temperature of the environment, T0 is the initial temperature of the object, and k is a constant that depends on the material properties of the object.
Solution
In this case: Te = 70 oF
First find k
From 9:15 to 10:00 (45 minutes) the body temperature changed from 83.6 to 80.3. Thus:
80.3 = 70 + (83.6 - 70)e-45k

Hence we can find the time of death using the temperature at 10PM
80.3 = 70 + (98.6 - 70)e-0.006176t
80.3 = 70 + 28.6e-0.006176t

Thus the time of death is 165 minutes before 10PM or at ~7:15PM