From noon to 1 pm:
The temperature rose from 75 to 77, so it rose 2 degrees.
From 1 pm to 2 pm:
The temperature remained constant at 75 degrees.
From 2 pm to 3 pm:
The temperature rose from 77 to 79, so it rose 2 degrees.
From 3 pm to 4 pm:
The temperature decreased from 79 to 78, so it decreased 1 degree.
From 4 pm to 5 pm:
The temperature rose from 78 to 81, so it rose 3 degrees.
So, the answer is "none"