solving polynomial function

i have to solve a polinomio of this form:

 

Z=A(x^2 y^2) + B(x^2 y) + C(x y^2) + D(x^2) + E(y^2) + F(xy) + Gx + Hy + I

 

i have all the constants and need to find the value of Z.

 

How can i do it?

 

Mauro