Question 1036326
You can think of this as one of the train being
stationary and the other train moving at the 
difference of their speeds
It takes 2 of their train lengths for the tail of
the moving train to pass the head of the
stationary one.
Let {{{ d }}} = 1 train length in km
{{{ 2d = ( 46 - 36 )*( 36/3600 ) }}}
( note that seconds are converted to hrs )
{{{ 2d = 10*( 1/100 ) }}}
{{{ 2d = 1/10 }}}
{{{ d = 1/20 }}} km
Convert km to meters
{{{ ( 1/20 )*( 1000/1 )  = 50 }}}
The length of each train is 50 meters
Hope I got it!