Modules & VBA :: Turnover Calculation On Monthly Basis

I am looking automation through VBA for the calculation of HR employees turnover on monthly basis, i have a query showing fields ..

employee name
joining date
department
section
employee left (Yes/No)
Left date

Now I am looking for;

i) Opening strength: Total employees strength through joining date with criteria of department and section wise at month start

ii) Closing Strength: Total employees strength through joining date with criteria of department and section wise at month end (subtracting the employees left through employee left field y/n)

iii)Left Employees: number of employees left at the end of each month with the criteria of department and section wise

iv) Turnover: The number of left employees will be divided by the dividend of (sum of opening & closing employees divided by 2)