If 3 is the middle term in the ratio of x and 9, then x = how much.
如果3是x和9的比例中项，那么x=多少．
<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">9 / 9</gadget>
<output>1</output>

<result>1</result>