Question 1105089
<pre>
                SPEED      TIME        DISTANCE

DONE              r         80/r          80

IF               r+3       80/(r+3)       80

DIFFERENCE                 {{{1&1/3}}}
</pre>


He took {{{80/r}}} hours for the trip.

{{{highlight_green(80/r-80/(r+3)=1&1/3)}}}

-

{{{80/r-80/(r+3)=4/3}}}

{{{20/r-20/(r+3)=1/3}}}

{{{60/r-60/(r+3)=1}}}

{{{60(r+3)-60r=r^2+3r}}}

{{{60r+180-60r=r^2+3r}}}

{{{180=r^2+3r}}}

{{{r^2+3r-180=0}}}

{{{(r-12)(r+15)=0}}}

-

{{{highlight_green(r=12)}}}


Time taken was  {{{80/12=40/6=20/3=highlight(6&2/3)}}}, hours.
6 hours 40 minutes