Question 615280
Plane  	speed	=x	mph					
wind   	speed	=y	mph					
against wind x-y		4	hours					
with wind x+y		3	hours					
								
Distance against wind	720	miles	distance with wind 720	miles	
t=d/r	against	wind						
720	/	(	x	-	y	)=	4	
4	(	x	-	y	)	=	720	
4	x	-	4	y	=	720	....................1	
with wind								
720	/	(	x	+	y	)=	3	
3	(	x	+	y	)	=	720	
3	x	+	3	y	=	720	...............2	
Multiply (1) by	3							
Multiply (2) by	4							
we get								
12	x	+	-12	y	=	2160		
12	x	+	12	y	=	2880		
24	x	=	5040					
/	24							
x	=	210	mph					
								
plug value of x in (1)								
4	x		-4	y	=	720		
840			-4	y	=	720		
-4	y	=	720	-840				
-4	y	=	-120					
	y	=	30	mph				
	plane speed	210	mph					
	wind speed=	30	mph