Solution ratio: 12: (3/5)=x: (1/2).
解比例：12：(3/5)=x：(1/2)．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">12 * (1/2)</gadget>
<output>6</output>

<gadget id="calculator">6 * 5</gadget>
<output>30</output>

<gadget id="calculator">30 / 3</gadget>
<output>10</output>

<result>10</result>