0.85
1) Since the exponential model of decay points out, in this case, a devaluation. then, we can write the following for a 15% decay:
![\begin{gathered} y=a(1-0.15)^{(t)/(12)} \\ y=a(0.85)^{(t)/(12)} \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/tho23ji2n1n9iaz1z27wtqn0l8eo2e6mmg.png)
Note that 1, refers to 100%. And a to the initial value.
2) So the base is 0.85 and a is the initial value. This function will provide us the devaluating value over time.