Given that the machine takes 80 minutes to produce 100 gallons of ice cream, so the rate of production (r) is given by,
[tex]\begin{gathered} r=\frac{100}{80} \\ r=1.25\text{ gallons/min} \end{gathered}[/tex]So the time required to produce 1200 gallons of the ice cream is calculated as,
[tex]\begin{gathered} t=\frac{1200}{r} \\ t=\frac{1200}{1.25} \\ t=960\text{ min} \end{gathered}[/tex]Thus, 960 minutes are required for producing 1200 gallons of ice cream.
Converting into hours,
[tex]\begin{gathered} 960\text{ minutes=}\frac{960}{60}\text{ hours} \\ 960\text{ minutes=}16\text{ hours} \end{gathered}[/tex]The time 16 hours after 6:00 am will be 22:00 which corresponds to 10:00 pm.
Therefore, the product run will end at 10:00 pm.