Question 873649
 <pre><font face = "consolas" color = "indigo" size = 3><b>
Hi
 t = D/r
{{{1000/(r-50) + 1000/(r+50) = 9/2}}}
     {{{2000r/(r^2 - 2500) = 9/2}}}
 9r^2-2000r -22500 = 0,  r = 450 mph
*[invoke quadratic "x", 9,-4000,-22500 ]