Question 833134
What same distance?  Taking your question just as you asked, the planes reach the same distance for time at which the distance of eastbound and westbound planes are equal.


Using Rate*Time=Distance
Eastward:  {{{350*t=d}}}
Westward:  {{{450*t=d}}}
Find t for when {{{350t=450t}}}
The question is nonsense.  These two planes will not reach the same distance of travel at the same time.



One of the questions often asked for a travel uniform-rates problem similar to this one is, where or when do the two planes meet: The Where, being how far from A to B or from B to A; and the When, being for how long do the planes fly if started at the same time until they meet.  Here is how this could be handled:


______________speed___________time___________distance
eastward______350_____________t______________350t
westward______450_____________t______________450t
Total________________________________________1000


You obtain sum of distances, {{{350t+450t=1000}}}
{{{800t=1000}}}
{{{t=10/8=5/4}}}
{{{t=1&1/4}}} hour, from which you can calculate either plane's distance.