Add 3 to the denominator of (3/5), how much should be added to the numerator to keep the size of the fraction unchanged.
(3/5)的分母加上3，要使分数的大小不变，分子应该加上多少．
<gadget id="calculator">5 + 3</gadget>
<output>8</output>

<gadget id="calculator">8 / 5</gadget>
<output>8/5 = around 1.6</output>

<gadget id="calculator">3 * (8/5)</gadget>
<output>24/5 = around 4.8</output>

<gadget id="calculator">(24/5) - 3</gadget>
<output>9/5 = around 1.8</output>

<result>9/5 = around 1.8</result>