用简便方法计算．
7.85+6.76+2.15           18.43﹣3.76﹣7.24        21.65+（4.8﹣3.65）
9.64﹣（4.64﹣1.23）     2.7+17.6+3.3﹣5.6       9.87﹣3.5+2.13﹣8.5．