a) (4-c) + 2(c-3)=-13
б) -3(3b+1)-12=12

(4-с)+2(с-3)=-13
4-с+2с-6=-13
с=-13-4+6
с=-11
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-3(3b+1)-12=12
-9b-3-12=12
-9b=12+3+12
-9b=27
b=27:(-9)
b=-3