So far I've got the formula working and it looks like this:

=SUMIF($B$1:$B$9639,"<=33",$C$1:$C$9639)

The problem is that I have to manually enter the "33", or whatever number I
need to be less or equal to, even though it is sitting in a cell just a few
columns away. If I try to link the cell the formula doesn't work anymore, and
just results in 0. The formula that doesn't work looks like this.

=SUMIF($B$1:$B$9639,"<=P9",$C$1:$C$9639)

Any suggestions would be appreciated, thanks.