Choice A is the correct answer. Solve for $t$ when $H(t) = 1000$.

1. Equation: $1000 = 100e^{0.12t}$.
2. Divide: $10 = e^{0.12t}$.
3. Natural log: $\ln(10) = 0.12t$.
4. Solve: $t = \frac{\ln(10)}{0.12} = \frac{2.303}{0.12} \approx 19.19 \approx 19.2$ months.

💡 Strategic Tip: Memorize $\ln(10) \approx 2.303$ for quick calculations.

Choice B is incorrect because this is too long. Choice C is incorrect because this is too short. Choice D is incorrect because this is way too long.