如题所述
1/2×6×(4+6)=30(cm²)
30-1/2(GB+6)×6=4GB×1/2
30-3(GB+6)=2GB
30-(3GB+18)=2GB
30-3GB-18=2GB
12-3GB=2GB
5GB=12
GB=2.4
4×2.4×1/2=4.8(cm²)
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