advanced formula for linking values in two sheets (differ.) under conditions

Hi! I attach 3 sheets with sample data and below I describe the problem I have - I mean the idea of what I want achieve, but don't know how to do it

The aim is to link the amount of days that someone is on holiday in particular month with the planned days in which he should work in the particular project running by my company.

1. the 'planning base' sheet descibes the percentage of involvement in the project
2. 'planning days' sheet describes involvement in days (working days*involvement)
3. the column named 8v, 9v, 10v, etc in the 'planning days' sheet should present the DIFFERENCE between column 8, 9, 10, etc and the planned vacations from sheet 'vacations' in the particular month.
4. Take note that the same person is involved in more than one project.
5. Example: in cell M3 I want to see: "11" - '10' (days of his holidays in August).

Could you please help me solve this challenge?

Thank you and regards,
Rita

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