Subtract 8 from the former term of the 12:6 ratio, how much should be subtracted from the latter term to keep the ratio unchanged
把12：6比的前项减去8，要使比值不变，后项要减去多少
<gadget id="calculator">12 / 6</gadget>
<output>2</output>

<gadget id="calculator">6 - 2</gadget>
<output>4</output>

<result>4</result>