If there is a fraction, add 2 to its denominator and reduce to 7/9; if add 3 to its denominator, reduce to 3/4, what is the original fraction?
有一个分数，将它的分母加上2，约简后得9分之7；若将它的分母加上3，约简得4分之3，那么原分数是多少．
<gadget id="calculator">3 - 2</gadget>
<output>1</output>

<gadget id="calculator">4 / 3</gadget>
<output>4/3 = around 1.333333</output>

<gadget id="calculator">9 / 7</gadget>
<output>9/7 = around 1.285714</output>

<gadget id="calculator">(4/3) - (9/7)</gadget>
<output>1/21 = around 0.047619</output>

<gadget id="calculator">1 / (1/21)</gadget>
<output>21</output>

<gadget id="calculator">7 / 9</gadget>
<output>7/9 = around 0.777778</output>

<gadget id="calculator">21 / (7/9)</gadget>
<output>27</output>

<gadget id="calculator">27 - 2</gadget>
<output>25</output>

<gadget id="calculator">21 / 25</gadget>
<output>21/25 = around 0.84</output>

<result>21/25 = around 0.84</result>