bjr de l aide pour cet exercice svp

a = 5/3  : 2/2+1/2 = 5/3 : 3/2 = 5/3 x 3/2 = 5/2

b = 9/12+4/12 : 6/3-7/3 = 13/12 :  -1/3 = 13/12 x -3/1 =  -13/4