Question 320546
first plane travels at an average speed of 240 miles per hour
second plane travels at an average speed of 320 miles per hour, 
 1400 miles apart?      

let them be 1400 miles apart after time t

distance traveled by plane A in time t = 240t
distance traveled by plane B in time t = 320t

..
320t+240t=1400
560t=1400
t=1400/560
= 2.5 hours