plot Piecewise[{{0, P < - 1.7807 / 0.7047}, {0.7047 * P + 1.7807, -1.7807 / 0.7047 <= P < 85.671 / 1.1118}, {1.8165 * P - 83.8903, P >= 85.671 / 1.1118}}] and 0.4535 * P + 1.4442

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