Question 1103620
As a native English speaker and former English teacher, I can say that the phrase "in still air" is acceptable and actually preferred. The phrase "at no wind" is awkward. The phrase "with no wind" could also be used.
r=w+184
r*t=d
With the wind
(r+w)*t=d
(r+w)*4=d
r=w+184
(w+184+w)*4=d
(2w+184)*4=d
8w+736=d
r=w+184
Against the wind
(r-w)*t=d
r=w+184
(w+184-w)*5=d
184*5=d
920=d  distance
8w+736=920
8w=184
w=184/8
w=23 mph wind speed
r=w+184
r=23+184
r=207 mph plane speed in still air or with no wind
check
(207+23)*4= (207-23)*5
230*4=184*5
920=920
ok