The denominator of (4/7) is increased by 14, how much should the numerator be increased to make the fraction value the original (1/2).
(4/7)的分母增加14，要使分数值是原来的(1/2)，分子应增加多少．
<gadget id="calculator">6 - 4</gadget>
<output>2</output>

<result>2</result>