Question 1044581
Travel Rates Rule, RT=D to relate rate, time, distance.


<pre>
               RATE        TIME       DISTANCE

SLOWCAR        r           t          d

FASTCAR       r+k          t          D

{{{system(k=10,d=60,D=90)}}}
</pre>


{{{system(d/r=t,D/(r+k)=t)}}}


{{{d/r=D/(r+k)}}}


{{{d(r+k)=Dr}}}


{{{dr+dk=Dr}}}


{{{dr-Dr=-dk}}}


{{{Dr-dr=dk}}}


{{{r(D-d)=dk}}}


{{{highlight(r=(dk)/(D-d))}}}--------purely symbolic formula answer.  Use the assigned values to evaluate r.