Acceleration of a system with three blocks

[duplaimp]

Homework Statement

What is the acceleration of this system?

Homework Equations

F=ma

The Attempt at a Solution

I tried the following:

Let blocks with mass 9kg, 4kg and 6kg be m9, m4, m6
This is the free body diagrams I drawn:

Then I applied Newton's 2nd Law:
F = ma

(For m9) mg-TR=9a
(For m4) TR-TL=4a
(For m6) TL-w*sin(30)=6a

I solved for a and it didn't gave the right answer.
What I am doing wrong?

 

[Doc Al]

(For m9) mg-TR=9a

Good.

(For m4) TR-TL=4a

What about gravity?

(For m6) TL-w*sin(30)=6a

Good.

Gravity applies to m4 just like it does to m6.

 

[duplaimp]

Gravity applies to m4 just like it does to m6.

I didn't included that because as m4 is "in the middle" I thought it wasn't necessary but it seems I was wrong. Now it gives the right acceleration.
Thank you!