Choice Choice B is the correct answer. This equation involves multiplication, so we use division to isolate the variable.

1. Start with the equation: $3x = 18$
2. Identify the operation: The variable $x$ is being multiplied by 3
3. Apply the inverse operation: Divide both sides by 3
4. Simplify: $x = \frac{18}{3} = 6$
5. Verify: $3(6) = 18$ ✓

💡 Key Concept: Multiplication and division are inverse operations. To undo multiplication by 3, divide by 3.

Choice Choice C is incorrect because this results from multiplying instead of dividing: $3 \times 18 = 54$. This is a common error when students apply the wrong inverse operation.

Choice Choice D is incorrect because this comes from subtracting 3 from 18 instead of dividing: $18 - 3 = 15$. Subtraction is not the inverse of multiplication.

Choice Choice A is incorrect because this results from adding: $18 + 3 = 21$. Remember, we need to divide to isolate $x$ when it's being multiplied.