The exponential function that describes the situation is given by:
y = 12 * (7/9)^x
where y is the value of the function, x is the independent variable, and 12 is the initial amount of the function. The factor (7/9) represents the decrease in the value of the function with each unit increase in x.
Note that as x increases, the value of (7/9)^x will become smaller and approach 0, so the value of the function will decrease towards 0.