We know that Mary works 3 days per week and Ana works 4 days per week. From Monday to Friday, there are 5 days in total. Since exactly two of them come to work each day, we can subtract the combined days that Mary and Ana work from the total number of days to find out how many days Nata works.
Since exactly two of them work each day, we can deduce that Nata must be working on the days when Mary and Ana are not working together. Mary works 3 days, which means there are 2 days left for Nata to work. Ana works 4 days, which means there is 1 day left for Nata to work.
Adding these days together, Nata works a total of 2 + 1 = 3 days per week. So, Nata works 3 days per week at the coffee shop.
