I don't understand!

Also

If the temperature was -9 degrees and it gets 9 degrees warmer then wouldn't it be 0 degrees?

we get the answer zero becoz when in integers when we add a postive integer and a negative integer then we have to subtract them and so if we subtact two same numbers like 9 then we het a zero!its just like 9-9=0

so 

(-9)+9

= -9+9 

= 0

just like 

9-9

= 0

okay!so i hope now u have understood !and if not then we're here to help you!

aww why didnt i think that!anyways i was just trying to give a " detailed" answer like you Melody so i wrote it!anyways nice example!

i'll give u a point for that!

Thanks Rosala.  

There are a lot of ways to explain this concept.  You gave a good answer  :)

thank you Melody!

or 

Its an honor to hear this from you my Queen!