Answer: -4.5 ℉
Explanation:
Given: On the coldest day of the year, the temperature at noon = 11℉
By midnight, the temperature had decreased by 15.5℉.
i.e. The temperature at midnight = Temperature at noon - 15.5℉
= 11℉ - 15.5℉
= (11-15) ℉
= -4.5 ℉
Hence, the temperature at midnight was -4.5 ℉.