8.5, since there are 2 significant digits, the only 2 numbers would be 8 and 4, so round at 4 since 5 isn't included by is above and equal to 5
Answer:
20 years.
Step-by-step explanation:
We have been given a formula
, which represents the value of an investment A (in dollars) after t years.
Substitute the given values:

Let us solve for k.


Take natural log of both sides:

Using property
, we will get:

We know that
, so

Dividing both sides by 1000, we will get:

Take natural log of both sides:







Divide both sides by
:


Therefore, it will take 20 years for the investment to be $9,000.