Randolph owns an apartment complex with six units. He charges $480 per month to rent one unit. Upkeep on the building costs Randolph $7,370 per year. If half of the rooms are filled continuously, how much will Randolph earn from his apartment complex over four years?

Half of the six units is 3 units. At $480 per month each, Randolph collects 3 × $480 × 12 = $17,280 per year; after $7,370 in yearly upkeep, he earns $17,280 − $7,370 = $9,910 per year. Over four years, that is 4 × $9,910 = $39,640, so the correct choice is $39,640.

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