Question 138999
{{{d[hs]}}} = miles from home to subway
{{{d[sj]}}} = miles from subway to job
{{{d[hj]}}} = miles from home to job  
I'll use the case where she bicycles all the way to work to find
the distance from her home to her job
{{{d[hj] = (12/60)*50}}}
{{{d[hj] = 10}}} mi
{{{d[hs] + d[sj] = 10}}}
{{{d[hs] = (12/60)*t[hs]}}}
{{{d[sj] = (24/60)*t[sj]}}}
{{{(12/60)*t[hs] + (24/60)*t[sj] = 10}}}
{{{t[hs] + t[sj] = 30}}}
{{{t[sj] = 30 - t[hs]}}}
substituting,
{{{(12/60)*t[hs] + (24/60)*(30 - t[hs]) = 10}}}
multiply both sides by {{{60}}}
{{{12t[hs] + 24*30 - 24t[hs] = 600}}}
divide both sides by {{{12}}}
{{{t[hs] + 60 - 2t[hs] = 50}}}
{{{-t[hs] = -10}}}
{{{t[hs] = 10}}}
{{{t[sj] = 30 - t[hs]}}}
{{{t[sj] = 30 - 10}}}
{{{t[sj] = 20}}}
{{{d[hs] = (12/60)*t[hs]}}}
{{{d[hs] = (12/60)*10}}}
{{{d[hs] = 2}}} mi
{{{d[sj] = (24/60)*t[sj]}}}
{{{d[sj] = (24/60)*20}}}
{{{d[sj] = 8}}} mi
It is 2 mi from her home to the subway stop. 
It is 8 mi from the subway stop from her job.