（1）31.5-18.54/1.8
=31.5-(18+0.54)/1.8
=31.5-18/1.8-0.54/1.8
=31.5-10-0.3
=21.2
(2)1.82/(0.13*0.7)
= 1.82÷0.7÷0.13
=2.6÷0.13
=20