Final answer:
The temperature at nightfall would be 0°F after a 7°F decrease from the morning temperature of 7°F.
Step-by-step explanation:
The question is asking for the temperature at nightfall after a decrease of 7°F from the morning temperature which was 7°F.
To find the temperature at nightfall, we subtract the temperature drop from the morning temperature.
Morning temperature = 7°F
Temperature drop = -7°F
Nightfall temperature = Morning temperature + Temperature drop
Nightfall temperature = 7°F + (-7°F)
Nightfall temperature = 0°F.