Question 389884
For Sally:
{{{d[s] = r[s]*t}}}
For Rocky:
{{{d[r] = r[r]*t}}}
Note that they start and finish together, 
so {{{t}}} is the same in both equations
------------------
given:
{{{r[s] = 110}}} km/hr
{{{r[r] = 90}}} km/hr
{{{d[r] + d[s] = 350}}} km
------------------
{{{d[s] = 110t}}}
{{{d[r] = 90t}}}
{{{90t + 110t = 350}}} km
{{{200t = 350}}}
{{{t = 1.75}}} hrs
check:
{{{d[s] = 110*1.75}}}
{{{d[s] = 192.5}}} km
and
{{{d[r] = 90*1.75}}}
{{{d[r] = 157.5}}}
{{{192.5 + 157.5 = 350}}}
{{{350 = 350}}}
OK