Subtract 4 from the numerator of (6/9), keep the fraction size unchanged, how much should be subtracted from the denominator
(6/9)的分子减去4，分数大小不变，分母应减去多少
<gadget id="calculator">6 - 4</gadget>
<output>2</output>

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">9 / 3</gadget>
<output>3</output>

<gadget id="calculator">9 - 3</gadget>
<output>6</output>

<result>6</result>