With Aliases
SELECT
SUM(rd.quantity * ISNULL(CAST(rd.rdActLbs / rd.quantity AS decimal(9, 2)), ISNULL(CAST(t.toActLbs / t.quantity AS decimal(9, 2)), ISNULL(CAST(po.poActLbs / po.unitQty AS decimal(9, 2)), rp.convPounds))) - ISNULL(dbo.tblRSTLine.rstQty, 0)) AS quantity, rp.convPounds...