For the train, moving along the curved rails, it can be written, with reference to the figure below, that
tanθ=Rgv2...(1)

Also, from the above figure, it follows that
tanθ=1.5h...(2)
Equations (1) and (2) imply that
1.5h=Rgv2⇒h=1.5×Rgv2=1.5×400m×10ms−2(12ms−1)2=0.054m=5.4cm