Final answer:
The temperature at 7:00 am was -19.3°C after a decrease of 6.3°C from the initial temperature of -13°C at midnight.
Step-by-step explanation:
To find the temperature at 7:00 am, we need to calculate how many times the temperature dropped by 0.9°C in a span of 7 hours. Since the temperature dropped 0.9°C each hour, we can multiply the rate of decrease by the number of hours elapsed.
Therefore, the temperature decreased by 0.9°C x 7 = 6.3°C from midnight to 7:00 am.
To find the temperature at 7:00 am, we subtract the decrease from the initial temperature at midnight.
-13°C - 6.3°C = -19.3°C