Final answer:
The equation that represents a proportional relationship is y = -3x.
Step-by-step explanation:
In this question, we are looking for the equation that represents a proportional relationship. A proportional relationship is one in which two quantities vary in a consistent ratio. In the given options, the equation that represents a proportional relationship is y = -3x (option A), because the y-value is directly proportional to the x-value with a constant ratio of -3.