Resolvemos aplicando la propiedad distributiva según sea el caso:
12-3{5-2[4-10(-1+8)-6(3-5)]+12}=
=12-3{5-2[4+(-10)(-1)+(-10)(8)+(-6)(3)+(-6)(-5)]+12}
=12-3{5-2[4+ 10 +(-80) + (-18) + (30)] + 12}
=12-3{5-2[4 + 10 - 80 - 18 + 30] + 12}
=12-3{5+[-2][4]+[-2][10]+[-2][-80]+[-2][-18]+[-2][30] + 12}
=12-3{5+[-8]+[-20]+[160]+[36]+[-60] + 12}
=12-3{5 - 8 - 20 + 160 + 36 - 60 + 12}
=12+{-3}{5}+{-3}{-8}+{-3}{-20}+{-3}{160}+{-3}{36}+{-3}{-60}+{-3}{12}
=12+ {-15} + {24} + {60} + {-480} + {-108} + {180} + {-36}
=12 - 15 + 24 + 60 - 480 - 108 + 180 - 36
= -3 + 84 - 588 + 144
= 81 - 444
= - 363