This question is conceived to make you waste your time. And frankly is not the top real close question for the GRE exam
Back to the question.
Look at just the first graph
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We need only to care of the two colors I have highlighted which represent the years from 40-59 and from 60-79
Moreover the question tells you that the range is between 20 and 60 %. Below 20% and above 60% do not count
Notice how of the two color only Arizona is shifted towards the right which is out of the range. Moreover, Arizona has the least amount,, if you do notice, of the two colors.
So in Arizona we must had the least amount of such units of real estate.
Regards