In City A, the temperature rises 7 degrees F from 8AM to 9AM. Then the temperature drops 6 degrees F from 9AM to 10AM. In City B, the temperature drops 2 degrees F from 8AM to 9AM. Then the temperature drop 4 degrees F from 9AM to 10AM. Write an expression that represents the change in temperature from 8AM to 10AM for each city. Simplify and interpret each sum.