(1)(-12)-(+8)+(-6)-(-5)
=-12-8-6+5
=-20-6+5
=-26+5
=-21
(2)(+3.7)-(-2.1)-1.8+(-2.6)
=3.7+2.1-1.8-3.6
=3.7-3.6+2.1-1.8
=0.1+2.1-1.8
=2.2-1.8
=0.4
(3)(-1.2)-(-2.1)+(-10.2)-(+0.5)
=-1.2+2.1-10.2-0.5
=0.9-10.2-0.5
=-9.3-0.5
=-9.8
(1)(-12)-(+8)+(-6)-(-5)
=-12-8-6+5
=-20-6+5
=-26+5
=-21
(2)(+3.7)-(-2.1)-1.8+(-2.6)
=3.7+2.1-1.8-3.6
=3.7-3.6+2.1-1.8
=0.1+2.1-1.8
=2.2-1.8
=0.4
(3)(-1.2)-(-2.1)+(-10.2)-(+0.5)
=-1.2+2.1-10.2-0.5
=0.9-10.2-0.5
=-9.3-0.5
=-9.8