Forces question help?

[Yoda]

A train of mass 40 tonnes has 3 carriages each with a mass of 20 tonnes. If the train is accelerating at 0.20ms^-2 calculate the tension in the chain of the last 2 carriages if each has a resistive force of 2000N.

[Thorium]

A train of mass 40 tonnes has 3 carriages each with a mass of 20 tonnes. If the train is accelerating at 0.20ms^-2 calculate the tension in the chain of the last 2 carriages if each has a resistive force of 2000N.

I am still learning this concept, so don't trust me too much.

F(net)=(2x20000)x0.2=T-(2x2000)
                           8000=T-4000
                                 T= 12000N

EDIT: Oh wait, is it talking about the very last chain or the 2nd last chain? I assumed it is the second last one. But if it is the very last one, the answer will be:
20000x0.2=T-2000
         4000=T-2000
               T=6000N