Question 1138064
r, speed of slow car
r+10, speed of  fast car


Time difference,  {{{(5/6)*hour}}}
{{{100/r-100/(r+10)=5/6}}}

.

.
{{{1200=r^2+10r}}}

{{{r(r+10)=1200}}}


Note that 30 and 40 are factors of 1200 and they differ by 10.


Slow Car,  30 mph
Fast Car,  40 mph