[tex]a)-21+49-13+7 = 49+7-21-15 = 56-36=\boxed{20} \\
b)-5 \times (-4)+27:3 = 20+9=\boxed{9} \\
c)84: (-4) +5 \times 3 =-21 + 15 = \boxed{-6} \\
d)(-8+7) \times 10+2^3 =-1 \times 10+8 = -10+8=\boxed{-2} \\
e)-72+ [8 \times (-9) +20 ] :2 =-72+ [-72 +20 ] :2 = \\
=-72-52:2 = -72-26 =\boxed{-98} \\
f) -36 : (-3) + 5^0 -1=12+1-1 = \boxed{12}[/tex]