Trying to sum distinct values SQL

I'm having trouble coming up with a value for a cell in SSRS, which should be a sum of distinct values. I have a SSRS report that looks similar to the below screenshot: I'm having trouble getting the value in red ($11.25). I basically need to sum the Ship Cost, based on distinct Tracking #s. So there are two distinct tracking #s, one with a Ship Cost of $5.25 and the other $6.00, so the total displayed in red should be $11.25. But I cannot achieve this in SSRS and can't figure it out in the SQL query either. I'm thinking a subquery like (and I know the below is not valid SQL): ``` (SELECT SUM([Ship Cost]) WHERE [Tracking #] IS DISTINCT) AS [Ship Cost] ``` But I don't know how to write it.