pouvez vous n°91 svp svp

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a = 1/2 + 3/2 x 7/3
a = 1/2 + 21/6
a = 3/6 + 21/6 = 24/6 = 4 

b = (1/2 + 3/2) x 7 /3
b =  4/2 x 7/3
b = 28/6 =  14/3

c = 20/9 - 10/9 = 10/9

d = (20/9 - 15/9) x 2/3
d = 5/9 * 2/3 = 10/27