Zend certified PHP/Magento developer

Needing help coming up with a formula to calculate salary expected to be used based on employee date hired and end date

I need help calculating salaries of employees on a monthly basis. I have start and end dates of the employees along with their annual salary. I need help coming up with a formula that will calculate the pay for the working days only. I made a quick example of how my worksheet is formatted. I need to do this until the year 2030 and would be super appreciative of a formula that will automate this process for me.
Thank you so much!! here is my example