Model coupling to 2D to 3D geomety (General Extrusion)

hello all,

I want to do a model coupling of 2D geometry and 3D.
For this i used general extrusion coupling for that.

I want to couple outlet ( along y axis) and inlet boundaries of 3D geometry through general extrusion coupling method. both geometries are of rectangle shapes.

I could not find suitable expressions for x and y in destination map in general extrusion couplings.

can anyone figure out equations of x and y in destination map for general extrusion coupling.??/

i have attached figure with this message.
looking forward for a reply
regards

Ali