A company noticed that the profit \( P \) they make from selling a product can be modeled by the quadratic function \( P(x) = -2x^2 + 40x - 150 \), where \( x \) represents the number of units sold (in thousands). To maximize profit, the company decides to increase its sales by a certain percentage. If the initial sales are 5,000 units, by what percentage should the company increase its sales to achieve maximum profit? Let's think step by step and output the final answer within \boxed{}.
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