42 %3D 2a %2Btb - 2c%2F3 - d%2F3%2C a %2B b %2B c %2B d %3D 58%2C a %2B b %3D 25%2C a %3E%3D0%2C b %3E%3D 0%2C c %3E%3D 0%2C d %3E%3D 0

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