Explanation:
the temperature drops 3°F per hour.
we start with 10°F.
so, how many hours is it dropping ?
noon = 12 pm (lunch time).
how many hours to 8 pm ?
well, 8 hours.
that means the temperature drops by 8×3 = 24°F.
therefore :
10 - 24 = -14°F
the temperature at 8pm will be -14°F.