Ok, So here's how I did it, might not be the easiest way, but it get's her done!

Imagine that the first plane is P1, the time of first plane is T1; speed is V1. Accordingly for the second plane it would be P2, T2, V2.

P1 has a total time of 2.25 hrs.

P2 has a total time of 2.25 hrs (135 mins) - 46 mins.. so 89 mins or 1.48hrs

If we say that V1 is equal to X + 50 (because it is 50mph faster in this case), and V2 is equal to X then we can produce the following formula

BUT! There is the time factor here. So we multiply these values by the appropriate T1 and T2

V1 is equal to 603.485 mph

V2 is equal to 603.485 mph + 50 mph = 653.485 mph

To Verify:

Multiply the V1 and V2 by the times to get

(603.485)(2.25) + (653.485)(1.48)

1357.841 + 967.158

= 2324.999

= 2325 miles

Hope this is clear and helpful!