not exactly sure what this question is asking but maybe this can help.

the speed of the plane when travelling with the wind is:

speed = distance/time = 1200/6 = 200 Km/h

the speed of the plane when travelling against the wind is:

speed = distance/time = 1200/8 = 150 km/h

so the plane travels at a speed 50 km/h less on average than it would flying with the wind.

does that help? or did you figure out that much already?