Question 1044966
p-w=5580/9=620 km/hr
p+w=6750/9=750 km/hr
add them
2p=1370
p=685 km/hr
substitute into first one
685-w=620
w=65 km/hr
check with second one
685+65=750 
plane goes 620 km/hr in still air 
the wind speed is 65 km/hr.