Question 845915
________________speed__________time__________distance
hway____________3r_____________(___)_________150
mountn__________r______________(___)_________50
TOTAL___________________________5____________200


R*T=D for Rate, Time, Distance; 
This means T=D/R allowing to find the missing time expressions.


________________speed__________time__________distance
hway____________3r_____________150/(3r)_________150
mountn__________r______________50/r___________50
TOTAL___________________________5____________200


The question asks, what is r, the speed on the mountain roads.  It is found using the time sum equation for this problem, {{{150/(3r)+50/r=5}}}, easily simplified to,
{{{150/(3r)+150/(3r)=5}}}
{{{300/(3r)=5}}}
{{{100/r=5}}};
and easily finished as {{{r/100=1/5}}};
{{{highlight(r=20)}}}