Bonjour

A = 3/8 x (1/3 + 7/9)

A = 3/8 x [(1 x 3)  /(3 x 3) + 7/9]

A = 3/8 x (3/9 + 7/9)

A = 3/8 x 10/9

A = 30/72

A = (6 x 5) / (6 x 12)

A = 5/12

B = 49/18 : 14/9

B = 49/18 x 9/14

B = 441/252

B = (63 x 7) / (63 x 4)

B = 7/4

C = 15/2 - 25/2 : 5/3

C = 15/2 - 25/2 x 3/5

C = 15/2 - 75/10

C = 15/2 - (5 x 15) / (5 x 2)

C = 15/2 - 15/2

C = 0

D = 7/15 : (1/5 - 8/5)

D = 7/15 : (- 7/5)

D = 7/15 x  (- 5/7)

D = - 35/105

D = (35 x - 1) / (35 x 3)

D = - 1/3.