A cup of hot coffee will, over time, cool down to room temperature. The principle of physics governing the process is Newton's Law of Cooling. The temperature (in degrees Fahrenheit) of a cup of coffee can be modelled by the following equation:
f(t)=80+120e^-0.08t

Explain, using the structure of the expression 80+120e^-0.08t, why the coffee temperature decreases as time elapses (8 points).