Electric Flux of a Non-Uniform Field

A non-uniform electric field is given by the expression $\vec{E} = (2xy)\hat{i} + (x^2)\hat{j} + (3z)\hat{k}$ N/C. What is the electric flux through a $2~\mathrm{m} \times 4~\mathrm{m}$ rectangle that lies in the xz-plane and is centered at the origin?