<em>4℉.</em>
What we know about Degrees is that there is a<em> </em><u><em>Positive</em></u> type and a <u><em>negative</em></u> type.
(i.e: 30℉ is <u><em>positive</em></u> and -30℉ is <u><em>negative</em></u>.)
If the temperature was -4℉ at 7AM, then it is negative. If it goes up by an amount that is more than 4 then that negative will go up to a positive temperature. In this case: At 9AM it was 8° <u><em>warmer</em></u>.
<u><em>Warmer</em></u><em> is a </em><u><em>keyword</em></u><u>.</u> If it is warmer by an amount, Negative temperatures <u><em>will go up to a positive</em></u> and positive temperature <u><em>will just go up</em></u>. If it gets cooler, negative temperatures <u><em>will go down further</em></u> and positive temperatures <u><em>will go down to a negative</em></u>.
So lets work out this problem with our newfound knowledge.
-4° F at 7AM
8° warmer at 9AM
-4 + 8 = 4.
<em>The temperature was 4° at 9AM.</em>
-Snooky