Subtract a from the numerator of the fraction (55/64), and add a to the denominator at the same time, the new fraction obtained after simplification is (4/13), then a=how much.
分数(55/64)的分子减去a，而分母同时加上a，所得的新分数化简后为(4/13)，那么a=多少．
<result>27</result>