"If you were" could say that you consider the person not smart enough now.
It could also mean the person was smart enough in the past event/situation/time.
If you were smart enough, you would have been in Honors Geometry. (But you are not smart enough, so you are not in that class.)
If you were smart enough to solve the first puzzle, how could the second one (which was easier) have given you trouble? (You did solve it, so you are smart enough.)
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