Question 1151413
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<pre>

Let x be the train's speed under the question.


Then the time equation is


    {{{30/x}}} + {{{30/(2x)}}} = {{{54/60}}}.


Multiply both sides by 60x. you will get


    1800 + 900 = 54x

    2700       = 54x

    x          = 2700/54 = 50.


<U>ANSWER</U>.  50 km/h.
</pre>

Solved.