You can't actually sum up objects you create on the form afaik. You can only sum the underlying data. But there are a couple of ways you can do what you are asking (if I understand correctly what you are asking !)
Assuming your report is based on a query, create two new columns in your query for F.S. Qty and M.S. Qty (using the formulas you've already got).
Add the two new columns to your report and you can sum as you would do normally.
In the footer (or wherever you are summing) add a text box with the control source as something like