Choice B is the correct answer. The initial value corresponds to $a$ in the standard form $y = ab^x$.

1. Identify: The standard form of an exponential function is $y = ab^x$, where $a$ is the initial value (y-intercept) and $b$ is the growth/decay factor.
2. Compare: In the given equation $y = 150(1.04)^x$, the coefficient $a$ is 150.
3. Conclude: Therefore, the initial value is 150.

💡 Strategic Tip: The initial value is always the number multiplying the power term. It represents the starting amount when $x=0$.

Choice A is incorrect because 1.04 is the growth factor $b$, not the initial value. Choice C is incorrect because 4 represents the percentage growth rate (4%), not the initial value. Choice D is incorrect because 156 is the value when $x=1$ ($150 \times 1.04$), not the initial value.