m-0.4+2m-1.8=3m-2.2
m一0.4十2m一1.8二3m一2.2
m-0.4+2m-1.8=m+2m-0.4-1.8=3m-(0.4+1.8)=3m-2.2
m-0.4+2m-1.8等于多少?m-0.4+2m-1.8=m+2m-0.4-1.8=3m-2.2