Math Help - Interest rate

An initial investment of $4000 doubles in value in 6.8 years. Assuming continuous compounding, what was the interest rate?

I would use the model



where A = annuities, P = principal amount invested, r = rate, t = time in years

Therefore



as the amount doubled over 6.8 years, using (t,A) = (6.8,8000) gives



Can you solve for r?

Spoiler:

Originally Posted by pickslides

I would use the model



where A = annuities, P = principal amount invested, r = rate, t = time in years

Therefore



as the amount doubled over 6.8 years, using (t,A) = (6.8,8000) gives



Can you solve for r?

Spoiler:

10.19% just what i was looking for