∵AD∥BC
∴△AOD∽△BOC
∴S△AOD/S△BOC=(OA/OC)²=25/64
OA/OC=5/8
∵△AOD和△COD在AC边上等高
∴S△AOD/S△COD=OA/OC=5/8
S△COD=8/5S△AOD=8/5×25=40