Question 701905
This is simply Rate*Time=Distance, for two trips for which both trips are the same Distance.  Easiest solution process is to create a table.


Let d be the distance ridden out in the country.

Format: RATE--------------Time---------------Distance
Out:____12---------------(?)  -----------------d
Return:__8---------------(??) ---------------d


How can we fill in the missing 'question marks for time? They'll be expressions. Rate*Time=Distance, so then Time=Distance/Rate.


Format: RATE--------------Time---------------Distance
Out:    12---------------( d/12)  ---------------d
Return:  8---------------( d/8) -----------------d


Total time given for both combined trips was 10 hours.

{{{d/12+d/8=10}}},   Solve for d.