Use the function Weekday(A1) to give the day of the week (Sunday=1,
Saterday=7)
If you haven't this function you have to activate the Add-Inn Analysis
Toolpak as follows:
Tools - Add-Inns - Analysis Toolpak
To calculate the number of Sundays and Saterday:
=CountIf(Range,1) + CountIf(Range,7)