4.已知长方体ABCD−A1B1C1D1ABCD-A_{1}B_{1}C_{1}D_{1}ABCD−A1B1C1D1中AB=3AB=3AB=3,AD=4AD=4AD=4,AA1=5AA_{1}=5AA1=5,用过该长方体体对角线AC1AC_{1}AC1的平面去截该长方体,则所得截面的面积最小值为((( )))