Question 437587
plane speed		x	mph				
wind speed		20	mph				
..							
against wind x-20	mph		
with wind  x+20	mph		
							
Distance against wind		350					
Distance with tail wind		420					
Time = same							
350/(x-	20)=420/(x+20)
350*(x+20)=420*(x-20)
350x+7000=420x	-8400
420x-350x=8400+	7000
70x=15400				
/70						
x=	220	mph