Question 858958
Let t = time going.
12-t = time returning, since the total of these times is 12.


Distance going is the same as distance returning.
RT=D for typical uniform rates travel.


{{{50t=70(12-t)}}}
{{{50t=840-70t}}}
{{{120t=840}}}
{{{highlight_green(t=7)}}};


Now, what can be done with the value for t?


... See?