Question 764208
Speed with wind = x + 40
Speed against wind = x - 40
470/x + 40 = 310/x - 40
Cross multiply
470(x - 40) = 310(x + 40)
470x - 18800 = 310x + 12400
470x - 310x = 12400 + 18800
        160x = 31200
           x = 195mph in still air.
Hope this helps.
:-)