It takes 40 days for team A and 50 days for team B to dig a tunnel alone. Now the two teams started excavating from one end of the tunnel, and finally met at a distance of 200 meters from the midpoint of the tunnel. How long is this tunnel in meters?
开凿一条隧道，单独开凿，甲队需要40天，乙队需要50天．现在两队各从隧道的一端开始开凿，结果在距隧道中点200米处相遇．这条隧道全长多少米？
<gadget id="calculator">1 / 40</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">1 / 50</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">(1/40) - (1/50)</gadget>
<output>1/200 = around 0.005</output>

<gadget id="calculator">(1/40) + (1/50)</gadget>
<output>9/200 = around 0.045</output>

<gadget id="calculator">1 / (9/200)</gadget>
<output>200/9 = around 22.222222</output>

<gadget id="calculator">(1/200) * (200/9)</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">2 / (1/9)</gadget>
<output>18</output>

<gadget id="calculator">200 * 18</gadget>
<output>3_600</output>

<result>3_600</result>