Cumulative calculation

I have these 2 tables that I attach.

A) Absences per employee, per month

B) Salary of each employee per month

Need:

1) Monthly cost of absence per employee = (gross + contributions of each month) / 30 days * number of days of absence that each employee has had in each month

2) Once this result has been obtained for each employee, for each month, add the monthly costs of each employee to reach the total costs due to the absence of the company. If possible, this calculation will accumulate as you filter per month.

I would appreciate suggestions.