Choice A is the correct answer. Substitute $m$ and $b$ into $y = mx + b$.

1. Given: $m = \frac{1}{2}$, $b = -4$.
2. Substitute: $y = (\frac{1}{2})x + (-4)$.
3. Simplify: $y = \frac{1}{2}x - 4$.

💡 Strategic Tip: Direct substitution into the slope-intercept form is the fastest way to write the equation.

Choice B is incorrect because it swaps the slope and y-intercept. Choice C is incorrect because it uses the reciprocal of the slope. Choice D is incorrect because it has the wrong sign for the y-intercept.