Question 1031863
{{{SPEED*TIME=DISTANCE}}}

{{{TIME=DISTANCE/SPEED}}}


<pre>
            SPEEDS         TIME            DISTANCE

WENT            r            16/r             16

BACK            r+4          16/(r+4)         16

DIFFERENCE                   2/3

40 minutes is {{{2/3}}} hour.
</pre>
{{{16/r-16/(r+4)=2/3}}}

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