Sarah has a storage box that she wants to fill with small cubes. The storage box has dimensions 12 feet in length, 8 feet in width, and 6 feet in height. Each small cube has a side length of 1 foot. However, due to a manufacturing defect, 10% of the small cubes are unusable. How many usable small cubes can Sarah fit into the storage box? Let's think step by step and output the final answer within \boxed{}.
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