Question 971286
Let x= speed of plane
Let y = speed of wind

9 (x-y)=  9x - 9y=8640 km   units km/h * hr for constant*variable
5 (x+y)= 5x + 5y =5900

Divide first by 9; divide second by 5

x-y=960 
x+y=1180  ;; now add them

2x = 2140
x=1070 km/h  still air speed
1070-y=960
y=110 km/h

add them (1180) ; multiply by 5=5900  km
subtract them (960), multiply by 9=8640 km 

Plane goes 1070 km/h
Wind speed is 110 km/h