$\"\"$

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The exponential decay function is $\"\"$ .

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The initial amount of chlorine is $\"\"$ .

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Twenty-four hours later, the amount of free chlorine is $\"\"$ .

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Hence, $\"\"$ and $\"\"$ .

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Substitute all the values in $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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The equation is $\"\"$ .

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Find the amount of free chlorine after threee days.

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

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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Therefore,the amount of free chlorine after threee days is $\"\"$ .

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$\"\"$

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Fid the time to reach thechlorine level to $\"\"$ .

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

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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Therefore, the chlorine level reaches $\"\"$ after $\"\"$ .

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$\"\"$

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The amount of free chlorine after threee days is $\"\"$ .

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The chlorine level reaches $\"\"$ after $\"\"$ .