Ineed with number 20. be sure to explain. you!

No its not correct
you would add 1 to both sides not subtract. and when you add -1 and -17 together it would equal -18

-16=-1+m
+1   +1

-15=m

now solve
>>  -16= -1+-15
       -16=-16

-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! :)

If you make you answer for clear i can answer it : )