I'm trying to write a sumif function where I add something if it is smaller
than or equal to a particular number. However, when I do this I need to
write the number in, instead of referencing the cell where the number is
located. Is there something extra I need to do.
This is what my formula looks like right now.

=SUMIF($T$9:$T$13,"<=13.5",$S$9:$S$13)

I want that 13.5 to be a cell, but excel is not working properly when I just
click on the cell. What can I add to the formula?