Réponse :
bonjour,
A = (-6)-(-12) - (+15) + (+6) + (-15) = -6+12 - 15 + 6 - 15 = -15-6-15+12+6 = -18
C = -18 + 13-(-7) + 14 - 20 = -18 + 13 + 7 + 14 -20 = -18 - 20 + 14 +7 +13 = -4
B = (+21)-(-3) + (-7) - (+13)-(-9) = 21 + 3 - 7 -13 + 9= -13 - 7 +21 + 3 +9 = 13
D = 3,8 - (-9) - 1,8 +1-(-4,5) = 3.8 + 9 - 1.8 + 1 +4.5 = -1.8 + 3.8 + 9 +1 +4.5 = 16.5
voila:)