丙=2912*0.5=1456 (立方米)甲=1456*6/(6+7)=672 (立方米)乙=1456*7/(6+7)=784 (立方米)
甲:乙:丙=6:7:136+7+13=26甲:2912*(6/26)=672(立方米)乙:2912*(7/26)=784(立方米)丙:672+784=1456(立方米)
丙=2912*0.5=1456甲=1456*6/(6+7)=672乙=1456*7/(6+7)=784