ANSWER:
M = 5
Step 1: Add 1 to both sides of the equal sign
-6m-1+1=31+1
-6m=-30
Step 2: Divide both sides by -6
-6m/6 = -30/-6
(Note: Both -6 values (The denominators) will cancel each other out, which is why the end result is 5 so, again, M=5)