Two planes are flying relative to each other from two cities at the same time, and they meet after 2 hours. The speed of one plane is 850 km/h, which is 80 km/h faster than the other plane. How many miles is the air route between these two cities?
两架飞机同时从两个城市相对飞行，2小时后相遇，一架飞机的速度是850千米/时，比另一架飞机快80千米/时．这两个城市之间的航线长多少千米？
<gadget id="calculator">850 - 80</gadget>
<output>770</output>

<gadget id="calculator">770 + 850</gadget>
<output>1_620</output>

<gadget id="calculator">1_620 * 2</gadget>
<output>3_240</output>

<result>3_240</result>