if $mx+3|x+4|-2=0$ has no solutions, solve for $m$ 
If $mx+3|x+4|-2=0$ has no solutions, which of the following value could be $m$?
(A)5
(B)$-\frac{1}{2}$
(C)-3
(D)-6
(E)$\frac{10}{3}$

my attempt:
$$mx-2=-3|x+4| \\ m^2x^2-4mx+4=9x^2+72x+144 \\ (9-m^2)x^2+(4m+72)x+140=0$$
because the equation has no solutions, therefore
$$(4m+72)^2-4(9-m^2)140<0 \\ 576m^2+576m+144<0 \\ 4m^2+4m+1<0 \\ (2m+1)^2<0$$
maybe I made a mistake but I couldn't find it

Consider the fact that $|x+4|$ has 2 different possible values. For $x\geq-4$, it becomes $x+4$. For $x<-4$, it becomes $-x-4$. Divide the problem into 2 those two different cases.
For $x\geq-4$, the equation becomes $mx+3(x+4)-2=mx+3x+10=(m+3)x+10=0$. We obtain that $x=-\frac{10}{m+3}$. In order to make there exist no solution for $x$, the value of denominator shall be zero. Thus $m+3=0$ which implies that $m=-3$.
For $x<-4$, the equation becomes $mx+3(-x-4)-2=mx-3x-14=(m-3)x-14=0$. We obtain that $x=-\frac{14}{m-3}$. Similarly, in order to make there exist no solution for $x$, the value of denominator shall be zero. Thus $m-3=0$ which implies that $m=3$.
After getting two different values of $m$ from both cases, we shall check whether it is correct or not by inserting each value of $m$ and try to solve the equation. After checking the value of $m$, the only value that fulfill the requirement is $m=-3$.
