There are the same number of goldfish in the big and small fish tanks. If you take 4 goldfish from the small fish tank and put them in the big fish tank, the number of goldfish in the big fish tank will be twice that of the small fish tank. How many goldfish are there in the small fish tank?
大小鱼缸里放着同样多的金鱼，如果从小鱼缸里拿出4条放到大鱼缸里，大鱼缸金鱼条数就是小鱼缸的2倍，小鱼缸里原来有多少条金鱼．
<gadget id="calculator">2 - 1</gadget>
<output>1</output>

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

<gadget id="calculator">2 * 4</gadget>
<output>8</output>

<gadget id="calculator">8 + 4</gadget>
<output>12</output>

<result>12</result>