Question 1193693
Basic idea is  RT=D for R rate or speed, time T, and distance D.

You may sometimes handle the basic idea like
{{{RT=D}}}

{{{(RT)/R=D/R}}}

{{{T=D/R}}}


Your given example allows you to form two expressions of time, and question asks for their difference.


<pre>
                SPEEDS        TIMES              DISTANCE

GOING TO        r              200/r                200
RETURN          r-10           200/(r-10)           200

DIFF.                            1
</pre>
With that you can setup  {{{200/(r-10)-200/r=1}}} , and then simplify and solve.