3x7+7x=42 21+7x=42 7x=21 x=3
(x+4)除0.2=35 5x+20=35 5x=15 x=3
14.5x+25x=51 39.5x=51 x=51分39.5
8x（x+3.2）=64.8
(x-1.6)除11=2 x-1.6=22 x=23.6