19Adding and subtracting integers

At 6 a.m. the temperature was −7°C. By noon it had risen 12 degrees, and by midnight it had fallen 9 degrees from the noon temperature. What was the temperature at midnight?

The midnight temperature was −4°C. Starting at −7°C, adding the 12-degree rise gives 5°C at noon, then subtracting the 9-degree fall gives 5 − 9 = −4°C.