Question 113411
You're on the right track. 
You do not need to use the quadratic formula to solve this linear problem. 
That is the correct two equation.
{{{12/(x+5)=8/x}}}
{{{12x=8x+40}}}
{{{4x=40}}}
{{{x=10}}}
The runner runs at 10 mph, the bicyclist bikes at 15 mph.