Final answer:
The constant of proportionality (r) for the given equation y = rx is 5/6. The correct equation is y = 5/6x.
Step-by-step explanation:
The constant of proportionality (r) can be found by comparing the ratio between the values of the dependent variable (y) and the independent variable (x). In this case, the correct equation is y = 5/6x, which means that for every 6 units increase in x, y increases by 5 units. Therefore, the correct answer is A. r = 5/6, y = 5/6 x.