BD=1/3AB AB=3BD
BD=1/7CD CD=7BD
EF=EB+DF-BD=1/2AB+1/2CD-BD=1/2(AB+CD)-BD=1/2(3BD+7BD)-BD=5BD-BD=4BD
BD=1/4EF=1/4*6=3/2
AB=3BD=3*3/2=9/2=4.5cm
CD=7BD=7*3/2=21/2=10.5cm
BD=1/3AB AB=3BD
BD=1/7CD CD=7BD
EF=EB+DF-BD=1/2AB+1/2CD-BD=1/2(AB+CD)-BD=1/2(3BD+7BD)-BD=5BD-BD=4BD
BD=1/4EF=1/4*6=3/2
AB=3BD=3*3/2=9/2=4.5cm
CD=7BD=7*3/2=21/2=10.5cm