The sum of the numerator and denominator of a fraction is 77. If 2 is added to both the numerator and denominator, the resulting fraction is (4/5) after division. What is the original fraction?
一个分数分子和分母的和是77，分子和分母都加上2，所得的分数约分后是(4/5)，则原来的分数是多少．
<gadget id="calculator">77 + 2 + 2</gadget>
<output>81</output>

<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">81 * (4/9)</gadget>
<output>36</output>

<gadget id="calculator">36 - 2</gadget>
<output>34</output>

<gadget id="calculator">5 / 9</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">81 * (5/9)</gadget>
<output>45</output>

<gadget id="calculator">45 - 2</gadget>
<output>43</output>

<gadget id="calculator">34 / 43</gadget>
<output>34/43 = around 0.790698</output>

<result>34/43 = around 0.790698</result>