well, let's keep in mind that the SAS postulate, so if one Side and the Angle next to it and the following Side after the angle are equal on both triangles, both triangles are congruent. Now, we have the angle 30° with sides and 9 and 2x and sides 9 and x + 4, well, the 9's are equal, dohh, you know, if only the 2x = x + 4, we'd be golden
[tex]2x = x + 4\implies 2x - x = 4\implies \boxed{x = 4}[/tex]
