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 400 km/h and Helicopter B flies to a certain place at a speed of 300 km/h. Helicopter A arrives 0.5 hours ahead of schedule and Helicopter B arrives 0.5 hours late. What is the flight distance from the base to a certain place in kilometers?
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400千米/小时的速度，乙直升机以300千米/小时的速度，飞往某地．甲直升机提前0.5小时到达，乙直升机迟到0.5小时．基地与某地的飞行距离是多少千米．
<gadget id="calculator">400 * 0.5</gadget>
<output>200</output>

<gadget id="calculator">300 * 0.5</gadget>
<output>150</output>

<gadget id="calculator">200 + 150</gadget>
<output>350</output>

<gadget id="calculator">400 - 300</gadget>
<output>100</output>

<gadget id="calculator">350 / 100</gadget>
<output>7/2 = around 3.5</output>

<gadget id="calculator">(7/2) + 0.5</gadget>
<output>4</output>

<gadget id="calculator">4 * 300</gadget>
<output>1_200</output>

<result>1_200</result>