This is the 4230th most frequent Polish word.
dodatkowymi
"Additional."
The word "dodatkowymi" is used here as an adjective describing the type of materials, specifically 'additional ones.'
Uczniowie otrzymali dostęp do dodatkowych materiałów.
The students received access to additional materials.
In this sentence, 'dodatkowymi' functions as an adjective describing 'seats', specifying that they are extra or additional ones for guests.
Przygotowaliśmy salę z dodatkowymi miejscami dla gości.
We prepared the room with additional seats for the guests.
Here, 'dodatkowymi' refers to the adjective describing 'experts', emphasizing their supplementary role in providing services.