Question 1131522
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..., 15 miles per hour faster in the morning which makes his 8 mile commute take 30 minutes {{{cross(less)}}} MORE time on the way home,...
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<pre>
                SPEED            TIME          DISTANCE

GOING            r+15            8/(r+15)       8

RETURN           r               8/r            8

DIFFERENCE                       1/2
</pre>

{{{8/r-8/(r+15)=1/2}}}------solve for r.