Question 881548
{{{TotalDistance/TotalTime=AverageSpeed}}}


{{{10/(4/40+6/r)=60}}}, all units based on kilometers, hours.  r is for travel speed for the last 6 kilometers.


{{{10/(1/10+6/r)=60}}}


{{{1/(1/10+6/r)=6}}}


{{{1/(r/10r+60/10r)=6}}}


{{{1/((r+60)/(10r))=6}}}


{{{10r/(r+60)=6}}}


{{{10r=6r+360}}}


{{{4r=360}}}


{{{highlight(r=90)}}}