Final answer:
The equation that is Not a proportional relationship is c. y = 6/x, which represents an inverse relationship rather than a linear one.
Step-by-step explanation:
The equation that is Not a proportional relationship is c. y = 6/x. A proportional relationship is a linear equation where the ratio of y to x is constant, which implies the equation can be expressed in the form of y = kx, where k is a constant coefficient.
The options a, b, and d represent linear equations where y is directly proportional to x. Option a has a negative proportional relationship with a constant factor of -6, option b has a positive proportional relationship with a constant factor of 1/7, and option d is a proportional relationship with a constant factor of 1/2.
In contrast, option c represents an inverse relationship, not a linear one, because as x increases, y decreases, and vice versa, which is not the case for proportional relationships.