请写出过程
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42. A 100*(95-x)=80*(100-x) = x=7543. B 21/x+4/y=12/x+7/y = x/y=344. A 3x=4*(x-5) = x=20 =20*5=10045. B 27-8-6-(5-2)-(3-2)-(4-2)-2=546. C 60*(6*60+20)/57=400min=6h40min = 11:1047. C 2V-Vo=V+Vo = V=2Vo & [L/(2V-Vo)]*2V=80 = L=6048. A (366+365)=731=7*104+3 = Monday49. B x-y=y-4; x-y=67-4 = x=46, y=2550. A 7+5+4+3+2=21