题目

阅读下面短文，然后根据要求完成短文后面的题目。(5分)   Wang Fengqin, a 61-year-old woman in Beijing, volunteers to sort（分类） rubbish in her living area in Beijing's Chaoyang District． At 6:30 every morning, while half of Beijing is still in sleeping dreams in bed or enjoying a delicious breakfast, Wang rushes through her busiest hours in the day. She gets up, gives her face a quick wash, takes a simple breakfast ,and rushes to the four rubbish dustbins beside the gate of her living area．There she checks the waste left by her neighbors to make sure it 同学孙华做了一道题：“已知两个多项式A和B，计算A-B”，可他由于粗心误将A-B看成了A+B，求得结果是9x2-2x+7，若B=x2+3x-2，请你帮助张华求出正确答案．