speed of plane in still air=207 miles/hr
Speed of air=23 miles/hr
Explanation:
let the speed of plane in still air=u
speed of wind=v
speed of airplane with the wind= u+v
so time taken= t= d/(u+v)
d= distance=920 miles
t=4 hours
so 4= 920/(u+v)
u+v=230 -----------(1)
speed of airplane against the wind= u-v
so time taken= t= d/(u-v)
d= distance=920 miles
t=5 hours
so 5= 920/(u-v)
u-v=184 -----------(2)
Adding equations (1) and (2)
u+v +u-v=230+184
2u=414
u=207 miles/hr
now u+v=230
207+v=230
v=23 miles/hr
so speed of airplane in still air= 207 miles/hr
speed of wind= 23 miles/hr