Let say that "x" was the temperature at the beggining of the day.
During the day, the temperature increased 6.8 degrees, so by the end of the day the temperature was "x+6.8"
Overnight the temperarure decreased 4.2 degrees, that is "x+6.8-4.2"
The overall temperature change is
[tex]6.8-4.2=2.6[/tex]The overall temperature change was 2.6 degrees
