Question 263619
This is an RTD problem. Here is a table  based on the given information
planes . . . . . . . .rate . . . . . . . time . . . . . . . .distance
to chi. . . . . . . . .400. . . . . . . . .T . . . . . . . . . 400T
from chi . . . . . . 500 . . . . . . . . 9 - T. . . . . . . 4500 - 500T
totals. . . . . . . . . . . . . . . . . . . 9 . . . . . . . . . . 
The distances must be equal, so we get
 400T = 4500 - 500T
add 500T to get
 900T = 4500
divide to get
T = 5
we now multiply 400*5 = 2000
it was a 2000 km trip


((((no offense to ur method of solving this but u forgot to add to get the total distance, 2000km is only half the distance for the round trip, total distance is 4000km for the whole trip. J.Barnum))))