The ratio of 12 to 19.5 is equal to the ratio of x to 6.5.
12与19.5的比等于x与6.5的比．
<gadget id="calculator">12 * 6.5</gadget>
<output>78</output>

<gadget id="calculator">78 / 19.5</gadget>
<output>4</output>

<result>4</result>