Bonjour,

6а - 4 = -1

6a = -1 + 4

6a = 3

a = 3/6

a = 0,5

9a + 6 = 13a + 14

9a - 13a = 14 - 6

-4a = 8

a = 8/-4

a = -2

5 - 3a = 4a - 2

5 + 2 = 4a + 3a

7 = 7a

a = 7/7

a = 1

7a = 63

a = 63/7

a = 9

4a + 9 = -39

4a = -39 - 9

4a = -48

a = -48/4

a = -12