If coefficient of $x^2{y}^3{z}^4$ in  ${(x+y+z)}^n$ is A, (where  $A\ne 0$) then coefficient  $x^4{y}^{4}z$ is 

Since $x_2{y}_3{z}_4$  is occurring in the expansion of (x +y +z)n, so n should be 9 only.
Now  
Coefficient of