（1）2.8x+x=1.71
3.8x=1.71
x=0.45
（2)30x+15x=22.5
45X = 22.5
X= 0.5
(3) 2.8+2x=22.6
2X= 22.6-2.8
2X=19.8
X =9.9
(4) 22.6-2x=2.8
-2X = -22.6+.2.8
-2X=-19.8
X =9.9
(5)（0.23-0.19）x 40×4+2x=400
6.4+ 2X =400
2X = 400-6.4
X =196.8
(6) 62×2+2x=358
124 +2X =358
2X =358- 124
2X= 234
X = 117