Here we have a function $g(t)=12.7e^{-0.098\cdot t}$ and another $f(t)=12.7 \cdot (e^{-0.098t}- e^{-3.29t})$.
$f(t)$ can be rewritten as $f(t)=g(t) - 12.7e^{-3.29t}$
Here are the graphs
I am trying to observe the resemblance of these two functions, but I fail to understand the interpretation of $f(t)$ in this case. First I thought that the function $f(t)$ could be shifted in some way by $12.7e^{-3.29t}$, which is the difference between $g(t)$ and$ f(t)$ but this is not a constant, it is a function itself. What does this difference represent and how to interpret it here?
Edit:
I suppose it is good to clarify the utility of these models. $f(t)$ is supposed to represent the concentration of a digested tabled in a body.
The function $y=12e^{-0.098t}$ describes the asymptotic behavior of the data, the values as $t$ becomes large, which apprear to be when $t>2$ in this model.
However, $g(t)$ does not account for the behavior of the data when $0\le t<2$.
For that data range the model must be adjusted by an amount $-e^{-3.29t}$.
This allows the model to account for the data when $t<2$ while having a negligible effect on the model for data when $t>2$ since $-e^{-3.29t}$ is small when $t>2$.