-16=-1+m
+1 +1
-15=m
Ryan's answer is wrong because he subtracted 1 instead of adding 1. You want to always get the variable by itself. If you subtract it the variable is not by itself:
-16=-1+m
-1 -1
-17=-2+m
Therefore, your final answer is -15. If you plug -15 into m you get: -16=-1+-15
which is a true statement.
Hope this helps! :)