what sum of money must be invested at 7.3% interest compounded continuously to yield $20,000 in 12 years
how long will it take for the investment to triple in value
$\displaystyle A=Pe^{rt}$
$\displaystyle 20000 = Pe^{0.073\times 12} \implies P = \frac{20000}{e^{0.073\times 12}} \implies P = 8329$
Now solve for $\displaystyle t $ where $\displaystyle 3\times 8329 = 8329 e^{0.073t}$
Is this what you found?
Spoiler:
first, the original investment is $\displaystyle P = 8328.91$.
now, read the original question again ...
the equation should be ...what sum of money must be invested at 7.3% interest compounded continuously to yield $20,000 in 12 years
how long will it take for the investment to triple in value
$\displaystyle 3(\textcolor{red}{8328.91})=\textcolor{red}{8328.9 1} \cdot e^{.073t}$
once again, note that the value of P will cancel, leaving you with the equation $\displaystyle 3 = e^{0.073t}$
who knows?
the OP has been bouncing back and forth between sites to find a solution ...
S.O.S. Mathematics CyberBoard :: View topic - compounded interest