Răspuns:
4×21+2×[100-6×(45-7×b)]=288-40
4×21+2×[100-6×(45-7×b)]=248
21+2×[100-6×(45-7×b)]=248:4
21+2×[100-6×(45-7×b)]=62
2×[100-6×(45-7×b)]=62-21
2×[100-6×(45-7×b)]=41
[100-6×(45-7×b)]=41:2
[100-6×(45-7×b)]=20,5
[6×(45-7×b)]=20,5+100
[6×(45×7×b)]=120,5
(45-7×b)=120,5:6
(45-7×b)=20,083
7×b=20,083+45
7×b=65,083
b=65,083:7
b=9,297
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