#### Answer

he required rate of interest is 10.99%.

#### Work Step by Step

Let us assume, $ A $ is the total amount, $ P $ is the principal amount, $ r $ is the rate of interest, and $ t $ is the number of years.
Therefore,
$\begin{align}
& A=\$18,000\\&P=\$6000\\&n=10\end{align}$
And the interest rate can be computed using the formula:
$\begin{align}
& A=P{{e}^{rt}} \\
& 18,000=6000{{e}^{10r}} \\
& {{e}^{10r}}=3 \\
& r=0.1099
\end{align}$
Therefore, the percentage rate of interest is:
$ r=10.99$ %