4: =4+5+{12+(-8)-(-8)-(-5)+(-12)+16-5+3}
=9+[12+5-12+16-5+3}
=9+19=28
5: =15-[13+8-10-16]-{5-7+9-3}
=15-(-5)-4
=15+5-4
=20-4
=16
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