\"\"

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The surface area \"\" of a hot-air balloon is \"\".

\

Radius of the balloon is \"\" where \"\".

\

Substitute \"\" in \"\".

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\"\"

\

Surface area of the balloon as a function of the time \"\" is \"\" where \"\".

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\"\"

\

Surface area of the balloon as a function of the time \"\" is \"\" where \"\".