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(a).

The revunue function is $\"\"$ .

The general form of quadratic equation is $\"\"$ .

Consider the two equations $\"\"$ , $\"\"$ .

Vertex is $\"\"$ .

Axis of symmetry $\"\"$ .

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Axis of symmetry is $\"\"$

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The maximum revenue is obtained when the unit price is $\"\"$ dollars

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The maximum revenue is obtained when the unit price is $\"\"$ dollars.