Let the flight distance be x,

According to the meaning of the question: x ÷ 1200+x ÷ 1500

Left and right times 6000: 6000× (x ÷1200)+6000× (x ÷1500) < = 6000× 2.5.

5X+4X & lt； = 15000

9X & lt= 15000

3X & lt= 5000

X & lt= 5000/3

We'll adopt it when it's settled. Thank you ~ ~ ~