Помогите решить 4 задание

Всм?

1.
.........=0.2x+8
x=5
0.2*5+8=18

2.
.......=2.9y+1
y=3
2.9*3+1=9.7

3.
........=6 2/3 a -7.8
a=1.5=15/10=3/2
20/3 * 3/2 - 7.8=2.2

4.
.........=7.4b-4.7
b=2.5
7.4*2.5 -4.7=13.8

5.
..........=12 - 0.3x
x=40
12-0.3*40=0

6.
.......=9-0.1a
a=90
9 - 0.1*90=0

7.
......=4b-a
a= -0.2,  b= -0.8
-4*0.8+0.2= - 3

8.
.........=9c - 3b=3(3c -b)
b= -0.1, c= - 0.7
3(-3*0.7+0.1)= - 3*2= -6

9.
..........=3d -6c=3(d-2c)
c=7/8 ,  d=2 3/4
3(2 3/4 - 2*7/8)=3*(11/4 - 7/4)=3 * 1=3

10.
.......=5m - 9n
m=1 1/2,  n=0.5
5*1.5 - 9*0.5=3

11.
..........=10b - 3a-2b+4a-b=7b+a
a=1 3/4,  b= -2 4/7
- 7 * 18/7+1 3/4= -18+1 3/4= - 16 1/4= - 16.25

12.
.......=12x - 4y -3x+5y-2x=7x+y
x= -13/14,  y=3.1
- 7 * 13/14 +3.1= -6.5+3.1= - 3.4