Surface integral question

Hey, I think the question is asking for a surface integral or maybe asking for you to use the divergence theorem but... does anybody have an idea of how to solve this problem?

(It's not coursework or anything, simply a past paper where the answer is -22.5)

"Evaluate $\int \int F \cdot n do$ where $y^2i-(x+2z)j+yzk$, S is the surface of the plane x+2y+2z=6 in the first octant, and n is the unit normal to the surface."

Any ideas?