7x+2x=0.81 4(x-6)=36 2x+0.2xX2=36 3.4x-6=4.2 7.8x+5=44 7.5x+

(1)7x+2x=0.81
9x=0.81. x=0.9
(2)4(x-6)=36
x-6=9. x=15
(3)2x+0.2x*2=36
2.4x=36. x=15
(4)3.4x-6=4.2
3.4x=10.2. x=3
(5)7.8x+5=44
7.8x=49. x=245/39
(6)7.5x+2.5=20
7.5x=17.5. x=7/3
(7)25.8-2x=12-7
2x=20.8. x=10.4
(8)4x+2.8=5.04
4x=2.24. x=5.6
(9)0.9-4*1.3=1.1
0.9x=6.3. x=7
(10)1.3*7=25-8x
15.9=8x. x=1.9875
(11)4.8+0.5x=6.3
0.5x=1.5. x=3
(12)(25+2x)*4=340
8x=240. x=30

x=0.09
x=15
x=15
x=3
x=5
x=3.3
x=10.4
x=0.56
x=7
x=0.51
x=3
x=120

. 别人先算好了..