1) The temperature at 9 a.m. was -10.3ºF, this is the initial temperature of the trial.
2) Between 9 a.m. and noon the temperature rose 9.6ºF, to determine what was the temperature at noon, you have to add 9.6ºF to the initial temperature:
The temperature at noon was -0.7ºF
3) Between noon and 3 p.m. the temperature went up 15.8ºF
To determine what was the temperature at 3 p.m. you have to add 15.8ºF to the temperature obtained in step 2
The temperature at 3 p.m. was 15.1ºF
4) Between 3 p.m. and 6 p.m. the temperature went down by 14.2ºF. To determine the temperature at 6 p.m., since the temperature decreased, you have to subtract 14.2ºF from 15.1ºF
The temperature at 6 p.m. was 0.9ºF