Question 1066676
Use time quantities instead of points in time.
<pre>
        SPEED         TIME        DISTANCE

SLOW       r           4+2=6        d

FAST      r+30         4            d
</pre>


{{{system((r)(6)=d,(r+30)(4)=d)}}}


The distances, each d, is the same.


{{{6r=4(r+30)}}}
Solve for r.