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r(R,b,q)= \left\{ \begin{array} {ll} (R−7000)(b−0.05R)−6000(q−b+0.05R); b−0.05R < q \\ (R−7000)q−4000(b−0.05R−q); \quad b−0.05R  ≥ q \end{array} \right.