0,2z-2/3z=-0.28                                        

z(2/10-2/3)=-0.28                                 

-14/30z=-0.28

z=-28/100:(-14/30)

z=3/5

 3(0.4x+7)-4(0.8x-3)=2

 1.2х+21-3,2х+12=2

 33-2х=2

2х=33-2=31

х=31:2

х=15,5 

 4.5(7/15x+2/9)-0.77(8/11x-3/7)=-1.75 

21/10х+1-56/100х+33/100=-1,75

2,1х+1-0,56х+0,33=-1,75

 1,54х+1,33=-1,75

1,54х=-1,75-1,33= -3,08

х=-3,08:1,54

х= -2

Verified answer

0,2z-2/3z=-0.28;

 2/10z-2/3z=-0,28

6/30z-20/30z=-0,28

-14/30z=-0,28

z= -28/100:(-14/30)

z=-28/100 *(-30/14)

z=60/100

z=0,6

3(0.4x+7)-4(0.8x-3)=2;

1,2x+21-3,2x+12=2

-2x=2-33

-2x=-21

x=21/2

x=10   1/2

4.5(7/15x+2/9)-0.77(8/11x-3/7)=-1.75

45/10*7/15x+45/10*2/9-77/100*8/11x+77/100*3/7=-1,75

21/10x+1-14/25x+33/100=-1,75

2,1x-0,56x=-1,75-1,33

1,54x=-3,08

 x=-2