Subtract 12 from the denominator of (15/18), how much should be subtracted from the numerator to keep the size of the fraction constant.
给(15/18)的分母减去12，要使分数的大小不变，分子应减去多少．
<gadget id="calculator">18 - 12</gadget>
<output>6</output>

<gadget id="calculator">18 / 6</gadget>
<output>3</output>

<gadget id="calculator">15 / 3</gadget>
<output>5</output>

<gadget id="calculator">15 - 5</gadget>
<output>10</output>

<result>10</result>