first subtract 4 from both sides
[tex]13 - 4 - 5m = - 6m[/tex]
then simplify
[tex]9 - 5m = - 6m[/tex]
add -5 to both sides
[tex]9 = - m[/tex]
since a variable shouldn't be negative the answer should be
[tex]m = - 9[/tex]
(I prefer having the variable on the left side)
