Centre of Mass

Good morning, I would need to know the conduct of the following exercise allocated for examining II Analysis at the university of Architecture.

exercise Text: A foil in the form of an isosceles trapezium has the bases of length 2 to 4 meters and the height of 2 meters. Knowing that the density p (x, y) is equal to the distance of the point (x, y) from the larger base, to determine the position of the center of gravity of such a foil.

I try to resolve, see images add. 

the result is correct, anyone can 'help me? thank you.