Summing values based on the criteria of an empty adjacent cell

Hi folks,
Bit of an excel noob here. I tried to search using the above title before posting, but I kept getting a fatal error.

What I am trying to do is add the total of column G (range is G3:G42) only where an entry does NOT exist in column N (range is N3-N42).

All I can find reference to is how to do this where there IS an entry in the adjacent (N) column.

Thanks for your help!