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The function is $\"\"$ .

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Where $\"\"$ is the number of minutes used.

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(a) $\"\"$ minutes :

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If $\"\"$ then the function is $\"\"$ .

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Substitute $\"\"$ in $\"\"$ .

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$\"\"$ .

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Monthly cost of the cellular phone for use of the $\"\"$ minutes is $\"\"$ .

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(b) $\"\"$ minutes :

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If $\"\"$ then the function is $\"\"$ .

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Substitute $\"\"$ in $\"\"$ .

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$\"\"$

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Monthly cost of the cellular phone for use of the $\"\"$ minutes is $\"\"$ .

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(c) $\"\"$ minutes :

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If $\"\"$ then the function is $\"\"$ .

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Substitute $\"\"$ in $\"\"$ .

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$\"\"$

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Monthly cost of the cellular phone for use of the $\"\"$ minutes is $\"\"$ .

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(a) $\"\"$ .

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(b) $\"\"$ .

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(c) $\"\"$ .