12.8 is the answer you can multiply 3.2 to 4 or you can add 3.2 to 3.2
A half hour is 30 minutes. So you would need to divide 30 by 5 and you get six. Multiple 6 degrees Fahrenheit by 6 and you get 36 degrees. The solution cooled 36 degrees in half an hour.
Hope this helps!
It’s 2x3x3x5 because 9 isn’t prime