I am trying to use the `=sum()` function in google sheets, and so far, that's all I have typed into the targeted cell. For example, I want D3 to be the sum of C2 and D2. I know how to type that. `=sum(C2,D2)`. But I want cells D3 thru D30 to have the same equation, relative to their adjacent cells. Something like this `=sum(cell to the left, cell above)`. Let me know if you need more elaboration, or if you have the answer, great!