Choice Choice A is the correct answer. When the variable is being divided, we multiply to isolate it.

1. Start with the equation: $\frac{x}{4} = 9$
2. Identify the operation: $x$ is being divided by 4
3. Apply the inverse operation: Multiply both sides by 4
4. Simplify: $x = 9 \times 4 = 36$
5. Verify: $\frac{36}{4} = 9$ ✓

💡 Key Idea: Division and multiplication are inverse operations. To undo "divide by 4", we multiply by 4.

Choice A is incorrect because this results from adding: $9 + 4 = 13$. Addition is not the inverse of division.

Choice B is incorrect because this comes from subtracting: $9 - 4 = 5$. Subtraction doesn't undo division.

Choice C is incorrect because this results from dividing 9 by 4 instead of multiplying: $\frac{9}{4} = 2.25$. This applies division again instead of using the inverse operation (multiplication).