According to this idea, the maximum temperature will drop by at least 10 degrees, which means-10+6=-4℃.
The minimum temperature drops by 20℃ at most, that is,-1℃+(-20℃) =-31℃.
Therefore, the highest temperature in this city will not be higher than -4℃ and the lowest temperature will not be lower than -3 1℃ the next day.