So your equation is m + 20 = 6
The first think you do is subtract 20 from both sides in order to get “m” alone, since that’s the variable you’re solving for. So what you’ll you have next is
m + 20 - 20 = 6-20
Since 20 subtracted by itself is zero, you’ll be left with
m + 0 = -14
Or more simply
m = -14