Car with counterweight: Dynamics

Hi,
There is something weird here:
Please look at problem and solution.

When I set my equations:
2000a=2000gsin(30°)-T
1800a=-1800gsin(20°)+T

I add them up:
3800a=2000gsin(30°)-1800gsin(20°)
a=1m/s^2

Now I want to equilibriate the car:
The force of brakes=-2000a=-2000a=-2000N.

But the book has a different answer. I understand their method. But why is my method wrong? Please try to explain to me in detail clearly. I have difficulty understanding.

http://ift.tt/1sXwPw4

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