Help in a very simple sum formula

Hi guys, i dont have much experience in excel, and im trying to do a simple formula and i googled it but cant find an answer.
I need to include a number in the sum formula plus the range. So i need to sum a range of cells + 900.
What i tried: =sum(I8:I38,900), =sum(I8:I38+900), =I8:I38+900. None of them worked.
It must be really simple i think. Thanks guys.