John sublets his apartment to 3 people who each pay $400 per month. He rents the apartment for $900 a month. How much profit does he make in a year?
Step-by-step reasoning process below:
3600
He gets 3 * $400 = $1200 per month.

So he gets 1200 * 12 = $14,400 per year.

So he pays 12 * 900 = $10800 a year.

That means his profit is 14400 - 10800 = $3600 per year.

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So, the final answer is 3600