Choice A is the correct answer. Solve for $r$ when investment quadruples.

1. Equation: $4P = Pe^{15r}$.
2. Simplify: $4 = e^{15r}$.
3. Natural log: $\ln(4) = 15r$.
4. Solve: $r = \frac{\ln(4)}{15} = \frac{1.386}{15} \approx 0.0924 = 9.24\%$.

💡 Strategic Tip: For quadrupling: $\ln(4) = 2\ln(2) \approx 1.386$.

Choice B is incorrect because this rate is too low. Choice C is incorrect because this rate is too high. Choice D is incorrect because this would more than quadruple.