Question 641936
Firstly move the z-term to the left side of the equation then multiply out the parenthetical expressions, yielding 
(1) mx + 2x + my - 8y - mz + 4z = 0
Now factor m out of term containing an m and get
(2) m*(x + y - z) + 2x - 8y + 4z = 0
Now factor a two out of the last three terms, and move the result to the right hand side and get
(3) m*(x+y-z) = -2*(x-4y+2z)
Now divide both sides by the coefficient of m on the left side and yield the answer
(4) m = -2*[x-4y+2z]/[x+y-z]  ; x+y-z not equal to zero