题目

 Mr Green             (teach) English in a middle school for ten years. 答案：has taught17．计算：（1）$\frac{{a}^{2}-4}{8{a}^{2}b}•\frac{12ab}{3a-6}$                       （2）$\frac{2}{x-2}-\frac{8}{{x}^{2}-4}$．