So if G is an undirected graph where the degree of each vertex is a multiple of 6 or 9 i have to show that the number of edges is a multiple of 3. 

where I am having trouble, I said that if the number of edges is equally divisible by 3 then the number of edges is a multiple of 3. 

I feel like this isn't enough....and I feel like I should be looking more closely at how the vertices have to be a multiple of 6 or 9 but I don't know how to relate this.

Just looking for hints and tips in the right direction; i feel like it's blatantly obvious but I can't see it