For this problem, I will assume that a majority of votes is sufficient to win.
step 1
Adds the percentages
32.9%+25.9%+20.0%+6.6%=85.4%
Divide by 2
85.4%/2=42.7%
so
If Raphael Warnock has a percentage greater than 42.7%
then
win the seat
The original percentage of Raphael Warnock is 32.9%
Find out the difference
42.7%-32.9%=9.8%
Applying proportion
Find out how many voters represent 9.8%
we know that
324,118 ------> 6.6%
so
324,118/6.6=x/9.8
solve for x
x=481,266 voters
therefore
the number of voters must be greater than 481,266 to win the seat