Answer
a. -2, b. -21
Work Step by Step
a. $16+(-9)+(-9)=16-9+(-9)=7+(-9)=7-9=-2$
b. $[3+(-13)]+[-4+(-7)]=[3-13]+[-(4+7)]=[-10]+[-(11)]=[-10]+[-11]=-(10+11)=-(21)=-21$
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