I found the answer for my other post from another forum, Thanks for those who looked.

the correct formula was:
=SUMIF(Demographics!$F$2:$F$212,$A2,Demographics!$ O$2:$O$212)

Anyway,

I do have another question. In the Total Sales worksheet, I have a a cell in S2 that I wish to show the max value from the "total sales" colum and then show the first and last name related to that particular row where the max value was. so, I only have =MAX(O2:O112), but I want to show the Name associated with the max and not just the $ amount.

So in S2 I want ---> John Doe and not $512.50, but I can only think of =IF(MAX(O2:O112), $B2+$B3, 0) becase I want both the first and last name. I used this formula with only $B2, but it just returned the first name in the B2 field