The purchase will depreciate to $4,000 in approximately 17 months. This is calculated by dividing the initial value ($12,000) by the monthly depreciation rate (5.34%). The formula for the time required is time = ln(final value/initial value) / ln(1 - monthly depreciation rate).
To determine the time it takes for a $12,000 purchase to depreciate to $4,000 at a monthly depreciation rate of 5.34%, we can use the formula for exponential decay. The formula is given by:

Here, the initial value is $12,000, the final value is $4,000, and the monthly depreciation rate is 5.34%.
Substituting these values into the formula:

Simplifying the expression gives:


Finally, the time required for the purchase to depreciate to $4,000 is approximately 20.1 months. Therefore, it will take approximately 17 months for the $12,000 purchase to depreciate to $4,000, considering a 5.34% monthly depreciation rate.