Get stuck with a simple math question and need your help.?

Here is the question:
If $5,000 is invested in a fund offering a rate of return of 12% per year, approximately how many years will it take for the investment to reach $10,000?
A. 4 years
B. 5 years
C. 6 years
D. 7 years

The right answer based on the key is C. 6 years. But as my opinion, I think it should be D. 7 years. I have no question for where the 6 years come from since the calcuation is very simple as:

5,000(1+12%)^N=10,000, the restult of N=6.116 years

From the mathmatical angle, N should be 6 years. However, the fact in the real life is the number couldnt reach 10,000 in year 6 even if it is very close to it. It is still 12/10=1.2 months over 6 years. Since the rate of return is paid annualy, so it at least take 7 years to reach the number 10,000.

What is your thought about it. feel confused now. Plz give me some help. Thank you.

But my question is not how come get the answer 6. Since the result is not exactly 6 but somewhat over it and the interest is paid annually. it means before year 7, it couldnt get reach 10,000 even at the year six. the number is very close to but not reach yet. It has to wait till the interest payment at year 7. I don't need the calcuation. I just need the explaination. Thank you.

That is the right answer. The Rule of 72. 72/ interest rate

So, 72/12%= 6 years.
Yep, that's it........