The two inner terms of the ratio are 12 and 3 respectively, one outer term is 2, and the other outer term is what.
比例的两个内项分别是12和3，一个外项是2，另一个外项是多少．
<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">3 * 6</gadget>
<output>18</output>

<result>18</result>