Question 110592
in this case, time=distance/rate ... let x="speed in still air"


(720/(x+30))+(720/(x-30))=10 ... 720(x-30)+720(x+30)=10(x^2-900) ... 1440x=10(x^2-900)


x^2-144x-900=0 ... (x-150)(x+6)=0