According to the meaning of the question: 5/2 (x+y) = 1200 ①

10/3(X-Y)= 1200 ②

Complete the equation: 3X+3Y= 1400 ③.

4X-4Y= 1440 ④

From ③: X=480-Y ⑤

Substitute ⑤ into ⑤ to get:

4(480-Y)-4Y= 1440

1920-4Y-4Y= 1440

1920- 1440=8Y

480=8Y

60=Y ⑥

Substituting 6 into 3 gives:

3X+3×60= 1440

3X= 1440- 180

X= 1260÷3

X=420

A: The average speed of the plane is 420 kilometers and the wind speed is 60 kilometers.

PS: I have some difficulty in writing math. You can also use addition and subtraction.