脱式计算．（怎样简便怎样算）
51.7+46.05÷1.5﹣9.3                             
857×1.9﹣8.57×80﹣85.7                  
÷（（+）×）                         
27×（+）×25 
45×（+﹣）                               
÷（4÷）+．