Start out with the parralle lines. What angles do you know are equal from these? And using the fact that these angles are equal, what triangles can you prove similar? And since you know that triangles are similar and the ration of one side is 2:5, what's the ration of the other sides?
"In the real world, this would be a problem. But in mathematics, we can just define a place where this problem doesn't exist. So we'll go ahead and do that now..."