12.如图所示,在棱长为2的正方体ABCD−A1B1C1D1ABCD-A_{1}B_{1}C_{1}D_{1}ABCD−A1B1C1D1中,点PPP在棱C1D1C_{1}D_{1}C1D1上,且BP=3BP=3BP=3,则点AAA,CCC到平面BB1PBB_{1}PBB1P的距离之和为((( )))