Terrific essay. A clear 6.
One thing that could have been better is where you suggest how to strengthen the argument -- you're very vague here, and specifics are always better. However, you'd written such a strong essay up to that point that it can't drag the score down.
Another thing to watch out for on test day is the desire to argue anything about reality. You're making an assumption in paragraph 4 that Boston's rent is higher than the rent in the other locations; don't do this. The only thing worth writing is that we don't know, and it COULD be that Boston is more expensive. You walk the line here between noting assumptions and arguing that the argument is "wrong," and you stay on the good side of the line here ... just be sure not to cross over on test day.
Overall, splendid essay, great job; do it like this on test day and you'll score a 6 for certain!
To anybody else reading this: Read this wonderful example of an Argument Essay before attempting your own. It doesn't have to be as long as ohfred's, but this is still a good ideal to shoot for.
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