Which equation represents a proportional relationship? a. y = 5x + 1 b. y=15x c. y=−x d. y=−5(x+1)

You know that two variables of an equation are related through direct proportionality when there is a constant value for their ratios. In equation form, a direct proportionality relationship is written as:

y = kx
where k can be any number

Therefore, the answer is B. In this case, k = 15.