Question 389200
Relative to the man on the train, the 2 trains are moving apart 
at the sum of their speeds, or {{{72 + 54 = 126}}} km/hr
Let {{{s}}} = the length of the other train.
In {{{8}}} sec, {{{s = 126*(8/3600)}}}km
(note that {{{3600}}} is the number of seconds in an hour)
{{{s = .28}}}km
{{{s = 280}}} m