Răspuns:
-4+a=-6
a=-6+4=>a=-2
_______
-3+a=-11
a=-11+3
a=-8
_________
a+(-2)=-12
a=-12+2
a=-10
________
a+(-7)=-20
a=-20+7
a=-13
(-4) + (-2) = -6
-3 + (-8) = -11
-10 + (-2) = -12
-13 + (-7) = -20
