please help me how to find it

Question

a)Find the time it takes for $8,500 to double when invested at an annual interest rate of 9%, compounded continuously.

b)Find the time it takes for $850,000 to double when invested at an annual interest rate of 9%, compounded continuously.

Answer 1

2 = e^0.09t

ln 2 = 0.09t

0.69314718 ≈ 0.09t

7.70 ≈ t

Note: The doubling time is the same for all starting amount.