Bonjour,

a. 3 (x - 2) + 6 (4 - x)

= 3x - 6 + 24 - 6x

= 3x - 6x - 6 + 24

= - 3x + 18

b. 6 (1/3x + 1) - 12x

= 6/3x + 1 - 12x

= 2x + 1 - 12x

= 2x - 12x + 1

= - 10x + 1

c. 3/4 (- 12x + 16/5)

= - 36/4x + 48/20

= - 9x + 12/5

d. 2 (x + 1/2)  - 3 (x + 1)

= 2x + 2/2 - 3x - 3

= 2x + 1 - 3x - 3

= 2x - 3x + 1 - 3

= - x - 2.