Question

How do I solve a problem like this? 

m-4=2m

Answer 1

$m-4=2m\ \ \ |Subtract\ m\ from\ each\ side\\\\ -4=m\\\\ m=-4\\\\Solution\ is\ m=-4$

Answer 2

m = -4

m-4=2m
-4+m=2m (reorder) 
-4 + 1m + -2m = 2m + -2m (added -2m to both sides)
-4+ -1m =0 (added like terms)
-4 +4+ -1m = 0+4 (added 4 to each side)
-1m = 4
m=-4 (divided by -1)