Question 74970
time = distance/rate
s = speed of plane in still air


This leads to   {{{650/(s+35)+1=650/(s-35)}}} or {{{(650+s+35)/(s+35)=650/(s-35)}}}


cross multiplying gives {{{650s+s^2+35s-(650*35)-35s-35^2=650s+(650*35)}}}


Combining and rearranging terms gives  {{{s^2=1335*35}}} or s=216.16 mph