Question 826065
Here is help to start:


Change 25 minutes into hours, {{{25/60=highlight_green(5/12)}}} hours.


The situation can be described using Law Of Cosines,
{{{highlight_green(a^2+b^2-2ab*cos(gamma)=c^2)}}};


If one train follows a, then {{{a=(40*miles/hour)*(5/12)*hour}}};
and the other train follows b, {{{b=(55*miles/hour)(5/12)*hour}}}.
You would be calculating, then computing c.