Subtract a from the numerator of the fraction (53/79), add a to the denominator, and the fraction is equal to (4/7), then what is the natural number a?
将分数(53/79)的分子减去a，分母加上a，约分后等于(4/7)，则自然数a等于多少．
<gadget id="calculator">53 + 79</gadget>
<output>132</output>

<gadget id="calculator">4 + 7</gadget>
<output>11</output>

<gadget id="calculator">132 / 11</gadget>
<output>12</output>

<gadget id="calculator">12 * 4</gadget>
<output>48</output>

<gadget id="calculator">53 - 48</gadget>
<output>5</output>

<result>5</result>