A base has A and B emergency helicopters to carry out rescue missions in mountainous areas. On a certain day, Helicopter A flies to a certain place at a speed of 400km/h and Helicopter B flies to a certain place at a speed of 300km/h. Helicopter A arrives 0.5h ahead of schedule and Helicopter B arrives 0.5h late. How many kilometers is the flying distance between the base and a certain place?
某基地设有甲、乙应急直升飞机，执行山区抢救任务．某日，甲直升机以400km/h的速度，乙直升机以300km/h的速度，飞往某地．甲直升机提前0.5h到达，乙直升机迟到0.5h．基地与某地的飞行距离是多少km？
<gadget id="calculator">0.5 + 0.5</gadget>
<output>1</output>

<gadget id="calculator">1 / 300</gadget>
<output>1/300 = around 0.003333</output>

<gadget id="calculator">1 / 400</gadget>
<output>1/400 = around 0.0025</output>

<gadget id="calculator">(1/300) - (1/400)</gadget>
<output>1/1_200 = around 0.000833</output>

<gadget id="calculator">1 / (1/1_200)</gadget>
<output>1_200</output>

<result>1_200</result>