Answer:
You can tell because, as x increases/decreases, y increases/decreases at the same rate EACH TIME. This way, no matter how many times the proportions increase OR decrease, the ratio between x and y always stays the same.
Did you just state the answer? Because it seems like you just answered the question for us.
See the attached picture:
The Answer is C 5/6
250/300 reduced and simplified is 5/6