Where you went wrong:
Instead of adding 30 to -48, you subtracted 30 from -48 and you ended up with -78.
Correct answer with explanation:
-48 + 30 = -18
Simply add 30 to -48, or a more intuitive would be to subtract 30 from positive 48 and then remembering the problem was -48 + 30 so adding the negative sign to get -18.
