Subtract 9 from the former term of 12:8, how much should be subtracted from the latter term to keep the ratio constant
把12：8的前项减去9，要使比值不变，后项要减去多少
<gadget id="calculator">12 - 9</gadget>
<output>3</output>

<gadget id="calculator">12 / 3</gadget>
<output>4</output>

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

<gadget id="calculator">8 - 2</gadget>
<output>6</output>

<result>6</result>