So doc height: dcb height = 1:2.

So doc height: aob height = 1:2.

Because trapezoidal abcd

So doc and aob are similar triangles.

So Sdoc:Saob= 1:4.

So SDOC: SABC = SDOC: (SCOB+SAOB) =1:(4+2) =1:6.

End ~

I didn't expect to remember math after so many years ~