How to change change formulas such that formula is based on Work Days rather than Days

[Holan95]

Hi Excel Forum members,
I have a schedule that has formulas that calculate end dates based on the number of days (including weekends) that a task takes to complete. Entering in the number of days calculates the end date as well as the number of work days to finish the task. However, I want to do the opposite such that (with the same start and end dates, except cells C10 and C28 which should be Monday and Friday, respectively) entering in the number of work days spits out the number of days (including weekends) a task would take to complete. Would anyone have any suggestions on how to do this? Furthermore, regarding cells C10 and C28, would anyone know a formula that adds the next working day to a date rather than calendar day? Please see the attached sample spreadsheet.

Thanks!