4a+2=7+a /-a
3a+2=7 /-2
3a=5 / :3
a=5/3

3b+1=5+b /-b
2b+1=5 /-1
2b=4 / :2
b=4/2=2

5c-2=3c+4 /-3c
2c-2=4 /+2
2c=6 /:2
c=6/2=3

2a+5-3a-4+5a=2+2a-4
2a-3a+5a +5-4 = 2-4+2a
4a + 1 = -2 + 2a /-2a
2a + 1 = -2 /-1
2a = -3 / :2
a= -(3/2)

5-3b+6-2b+5b=2b-12b+5+10b
-3b-2b+5b + 5+6 = 2b-12b+10b +5
-5b+5b + 5+6 = 12b-12b +5
11≠5

4c-15+3c-6=5c-10+c-8
4c+3c -6-15 = 5c+c -10-8
7c - 21 = 6c -18 /+21
7c = 6c +3 /-6c
c=3