There are two cargo ships, A and B, and the cargo carried by ship A is three times that of ship B. If ship A increases its cargo by 1200 tons and ship B increases its cargo by 900 tons, then the cargo carried by ship A is twice that of ship B. Originally, How many tons does the ship carry?
有甲、乙两艘货船，甲船所载货物是乙船的3倍，若甲船增加货物1200吨，乙船增加货物900吨，则甲船所载货物是乙船的2倍，原来乙船载货多少吨？
<gadget id="calculator">900 * 2</gadget>
<output>1_800</output>

<gadget id="calculator">1_800 - 1_200</gadget>
<output>600</output>

<gadget id="calculator">3 - 2</gadget>
<output>1</output>

<gadget id="calculator">600 / 1</gadget>
<output>600</output>

<result>600</result>