We can convert the values to percentage values and since a circle is 360°, we can multipy the percentages with 360° to get the degrees. The total of day is all the the things added up:
18 degrees F because it dropped 12 degrees=10 hours x degrees=15 hours x is what you want to find out which is how many degrees it would drop in 15 hours. 12x15 then divided by 10 is 18.
