To determine on which day Clara would use a positive number to write the temperature, we need to know the temperatures for each day. Generally, positive temperatures are above 0°C (or 32°F).
If the temperatures provided in the table show any day with a temperature above this threshold, that would be the day she would use a positive number.
Please refer to the actual temperature values for Tuesday, Monday, Wednesday, and Thursday in order to select the correct day. Without the specific temperature data, I cannot provide a definitive answer.
If you have that data available, please share it, and I will help you identify the correct day.