Answer:
13°C
Explanation:
The number of hours that the temperature fluctuates is irrelevant to the problem.
This problem is asking how many degrees did the temperature increase in order to go back to 30°C after being decreased by 13°C.
Find the new temperature after it decreased:
If the temperature after decreasing is 17°C, it needs the same amount it was decreased by to go back to 30°C.
Therefore, the temperature subsequently increased by 13°C to go back to 30°C after being decreased by 13°C.