Choice A is the correct answer. Find the annual growth factor.

1. Total Growth: $\frac{4,000,000}{500,000} = 8$.
2. Formula: $4,000,000 = 500,000(b)^6$, so $b^6 = 8$.
3. Solve: $b = \sqrt[6]{8} = 8^{1/6} = (2^3)^{1/6} = 2^{1/2} \approx 1.414$.

💡 Strategic Tip: To find $b$, take the 6th root of the total growth factor.

Choice B is incorrect because this would give $(2)^6 = 64$. Choice C is incorrect because this is the total growth, not annual. Choice D is incorrect because$(1.5)^6 \approx 11.39 eq 8$.