Choice A is the correct answer. Find when the investment doubles.

1. Target: Double means $A = 2 \times 15000 = 30000$.
2. Equation: $30000 = 15000(1.07)^t$, so $(1.07)^t = 2$.
3. Estimate: Test values:
   • $t=10$: $(1.07)^{10} \approx 1.967$ (close to 2)
   • $t=11$: $(1.07)^{11} \approx 2.105$ (over 2)
4. Answer: About 10-11 years, so "About 10 years".

💡 Strategic Tip: Rule of 72: doubling time ≈ $\frac{72}{7} \approx 10$ years.

Choice B is incorrect because doubling happens sooner. Choice C is incorrect because this is the interest rate, not doubling time. Choice D is incorrect because doubling occurs much earlier.