Expansion of an expression. I want to know how to expand expressions like $(x+y+z)(a+b+c)$, I currently have a problem I want to solve but I know FOIL if it is $(x+y)(a+b)$ but what do I do when it is $(x+y+z)(a+b+c)$?

Use the distributive property. 
We have that 
$$(x+y+z)(a+b+c)=x(a+b+c)+y(a+b+c)+z(a+b+c)$$ 
Can you continue? 
