$\"\"$

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The revenue function is $\"\"$ .

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Monthly selling cost function is $\"\"$ .

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(a).

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How many wrist watches have to sell for maximum revenue.

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The revunue is $\"\"$ .

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

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

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Vertex is $\"\"$ .

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Axis of symmetry $\"\"$ .

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$\"\"$

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$\"\"$

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The maximum revenue is obtained when there are $\"\"$ watches are sold out.

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Therefore,the maximum revenue :

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$\"\"$

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$\"\"$

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$\"\"$

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The maximum revenue is $\"\"$ dollars.

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$\"\"$

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(b).

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The profit function is $\"\"$ .

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Substitute $\"\"$ and $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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The profit function is $\"\"$ .

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$\"\"$

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(c).

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How many watches to sell to maximum profit.

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The profit function is $\"\"$ .

\

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

\

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

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Vertex is $\"\"$

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Axis of symmetry $\"\"$ .

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$\"\"$

\

$\"\"$

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$\"\"$ watches need to sold out to get maximum profit.

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The maximum profit :

\

$\"\"$

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$\"\"$

\

$\"\"$

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The maximum profit is $\"\"$ dollars.

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$\"\"$

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(a)To obtain maximum revenue,the shop keeper must sell $\"\"$ watches and the maximum revenue is $\"\"$ dollars.

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(b) The profit function is $\"\"$

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(c).To obtain maximum profit ,the shop keeper must sell $\"\"$ watches. and the maximum profit is $\"\"$ dollars.