Question 1080922
Let A be the northbound train, B the southbound.
1.{{{R[A]=10+R[B]}}}
The distance covered by A was,
{{{D[A]=R[A]*t=6*R[A]}}}
The distance covered by A was,
{{{D[B]=R[B]*t=3*R[B]}}}
The distance between them is,
{{{D=D[A]+D[B]}}}
{{{6R[A]+3R[B]=330}}}
Substituting from 1,
{{{6(10+R[B])+3R[B]=330}}}
{{{60+6R[B]+3R[B]=330}}}
{{{9R[B]=270}}}
Solve for {{{R[B]}}}.
Then use either equation to solve for {{{R[B]}}}.
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Is the graph displaying distance traveled versus time?
If so then, between {{{t=0}}} and {{{t=3}}}, 
{{{D=D[A]=R[A]*t}}}
Then {{{t>3}}},
{{{D=(R[A]+R[B])*t}}}