Let us suppose it will take t hours for the temperature to drop at least 36°F.
We have been given that temperature in Antarctica will decrease 8°F each hour for the next 6 hours.
And we have to find the time to drop the temperature to at least 36°F. At least means greater than equal to.
Therefore, we have the below inequality

Now, we solve the inequality.
Divide both sides by 8, we get

Hence, it will take atleast 4.5 hours to drop the temperature to 36°F.