Answer:
About 8.2 years.
Explanation:
The minivan was purchased for $35,000 and it depreciates according to the function:

Where t is the time in years.
And we want to determine how long it will take for the minivan to depreciate to 15% of its initial value.
First, find 15% of the initial value. This will be:

Therefore:

Solve for t. Divide both sides by 35000:

We can take the natural log of both sides:

Using logarithmic properties:

Therefore:

So, it will take about 8.2 years for Tenzin's minivan to depreciate to 15% of its initival value.