=18.9*178.178+0.49-17.8*（189+0.18）
=18.9（178.178-178）+0.49-17.8*0.18
=18.9*0.178+0.49-17.8*0.18
=0.178*（18.9-18）+0.49
=0.178*0.9+0.49
=0.6502