Respuesta :

gmany

Answer:

9

Step-by-step explanation:

(-)(-) = (+)

(-)(+) = (-)

(+)(-) = (-)

(+)(+) = (+)

-(-21) = (-)(-21) = (+)21 = 21

-12 - (-21) = -12 + 21           use commutative property: a + b = b + a

= 21 + (-12) = 21 - 12 = 9

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