So the way I would go about solving this issue would be to compare Celsius to Fahrenheit.
Zero degrees Celsius is 32 Fahrenheit, hence if the temperature was 32 Fahrenheit and one wanted to know how cold it would be if it was twice as cold the next day, I presume that the answer would be 0 degrees Fahrenheit which would convert to -17.78 degrees Celsius.
So the answer to the question according to my logic would be -17.78 Celsius.
Not sure if it makes sense. But let me know if you have a better solution.