Bonjour,

7)

x + 11 = 9

x = 9 - 11

x = - 2

8 + x = 10

x = 10 - 8

x = 2

2,5 + x = 4

x = 4 - 2,5

x = 1,5

x - 11 = 3

x = 3 + 11

x = 14

x - 5,9 = 7

x = 7 + 5,9

x = 12,9

x - (- 6) = 12

x + 6 = 12

x = 12 - 6

x = 6

10)

2x = 7

x = 7/2

x = 3,5

- 8x = 15

x = - 15/8

1,4x = 16

x = 16/1,4

x/7 = 6

x = 6 * 7

x = 42

x/13 = - 5

x = - 5 * 13

x = - 65

x/- 4 = 3

x = 3 * - 4

x = - 12

13)

5x + 1 = 16

5x = 16 - 1

5x = 15

x = 15/5

x = 3

2x - 9 = 17

2x = 17 + 9

2x = 26

x = 26/2

x = 13.