Warehouse A stores 20 tons of grain, and Warehouse B stores 16.4 tons of grain. After Warehouse B transports part of the grain to Warehouse A, Warehouse A stores exactly three times as much grain as Warehouse B. How many tons of grain does Warehouse B ship to Warehouse A?
甲仓库存粮20吨，乙仓库存粮16.4吨．乙仓库运给甲仓一部分粮后，甲仓存粮正好是乙仓的3倍，问乙仓运给甲仓多少吨粮食？
<gadget id="calculator">20 + 16.4</gadget>
<output>36.4</output>

<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">36.4 / 4</gadget>
<output>9.1</output>

<gadget id="calculator">16.4 - 9.1</gadget>
<output>7.3</output>

<result>7.3</result>