Bonsoir,
A= -31 + 15 -(-12)+21-7
= -16-(-12)+21-7
= -4 + 21 - 7 ( -16-(-12) c'est comme -16+12)
= 17-7
=10
B= 25-2+18-14+6-16
= 23 + 18 -14 +6 -16
= 41 - 14 + 6 -16
= 27 + 6 -16
= 33 - 16
= 17
C= -8 - (-14) -99 + 100
= -8 + 14 - 99 +100
= 6-99+100
= -93 + 100
= 7
D= 3-7 - (+3) - (-7)
= -4 - 3 + 7
= -7 + 7
= 0