We have to find the exponential model that best represents the data.
We can write a general model as:

Where A is the initial value: the value of f(x) when x = 0.
In this case, from the table, we can see that when x = 0. f(x) = 5, so A has to be 5.
We can also see that the value of f(x) is decreasing with the increase of x. This indicates that the value of b is less than 1.
We can find the value of b as:

Then, if we take x = 0, we can calculate b as:

We can write the exponential model as:

Answer: f(x) = 5(0.2)^x