Adding working days on weekends to a gantt chart

Hi,

I have been trying to build a simple gantt chart in excel to use in work. I've basically just edited the built in templates provided with Excel. Someone on here gave me some formulas to include an end date rather than plan duration, and a formula to exclude weekends as working days. They told me there is a way to include weekends on certain projects by typing a W on that day which would tell excel to highlight that day as a working day. However, I cant seem to work out how to do it with the formula they provided. Probably because I've amended the Gantt chart slightly.

Can anyone please help me out with this? I've uploaded the latest chart here so you can check it out.