The same:

S△ODC/S△OBC=DO/BO=S△ODC/9

So:

DO/BO=S△ODC/9=4/S△OAB

Then: S△OAB*S△ODC=36.

The area of quadrilateral ABCD =S△OAB+S△OAD+S△OCD+S△OCB.

= 13+S△OAB+S△ODC

& gt= 13+2 radical sign (S△OAB*S△ODC)

= 13+2*6

=25

The minimum value is 25.