svp aider moi je ny arrive pas !! (le 49)

a = ( 15/10 +6/10) (15/12-16/12) = 21/10 x -1/12 = 21/120 = 7/40

c = 3/2+3/4 -4/3 = 18/12 +9/12-16/12 = 27/12-16/12 = 11/12

b = ( 8/6 -15/6) : ( - 8/12 +9/12) = -7/6 : 1/12 = -7/6 x 12 =-14

d = 4/3 -5/2 x -3/2  +3/4 = 4/3 + 15/4 +3/4 = 4/3 +18/4 = 4/3+9/2 = 8/6+27/6 = 35/6