This is the tricky part.
You should infer from the stem. Moreover, this GRE (or GMAT) is all about: a test of reasoning.
Quote:
In 1995 the number of students enrolled in public institutions of higher education was approximately how many times the number of students enrolled in private institutions of higher education?
From the bold part you might infer that you need the %. As such, the second graph.
Regards
Shouldn't you get the same answer if you use the first graph or the second? Shouldn't both of them give you the "approximately how many times" ratio they are looking for? What am I missing here?