A cup with a volume of $8$ fluid ounces is filled at a rate of $0.5$ ounces per second. However, a hole at the bottom of the cup also drains it at a rate of $0.3$ ounces per second. Once the cup is full, how many ounces of water will have drained out of the cup?

Let's think step by step and output the final answer within \boxed{}.
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