Question 316576
If you're going downwind, you add the wind's velocity (vw) to the plane's still air velocity:


Downwind:  v = 210+vw


If you're going upwind, you have to subtract the wind's velocity:


Upwind: v = 210-vw


Now use the formula D=VT, where D=distance, v=velocity, and t=time. We know that the times are the same, so isolate for t and set them equal to each other:


t = d/v


Dup/Vup = Ddown/Vdown


161/(210-vw) = 259/(210+vw)


Now cross multiply and solve for vw:


33810 +161vw = 54390 -259vw
420vw = 20580
vw=49


The wind's velocity is 49mph.