According to the given information, to find the new temperature in Boston, we need to add the temperature it was risen by. It means we need to add 9 °F to the temperature in Boston at 6:00 am:
The temperature in Boston at noon is 6 °F.
To find how much higher was the temperature in St. Louis than in Fairbanks, we need to find the difference between the temperature of these cities, this way:
St. Louis was 75 °F higher.