Question 501677
West bound plane	x 	mph						
East bound plane	x+	-80						
..								
They are going away from each other.								
								
So add up their speed.								
								
combined speed = x+x+-80			
(	2	x	+	-80	) 			
Time = 	4	hours						
Distance =   	2880	miles						
Distance = speed * time								
(	2	x		-80	)*	4	=	2880
8	x 		-320	=	2880			
8	x 	=	2880	+	320			
8	x 	=	3200					
/	8							
x=	400	mph	West bound plane					
East bound plane	400	+	-80	=	320	mph