Breakdown of Анна напишет договор с коллегой.
Анна
Anna
написать
to write (perfective)
договор
contract / treaty
с
with (also со)
Questions & Answers about Анна напишет договор с коллегой.
Why does коллега change to коллегой here?
The preposition с (meaning "with" someone or something) requires the following noun to be in the Instrumental case. For nouns ending in -а like коллега, the ending changes to -ой in this case.
What if the colleague is a man? Would the ending be different?
No, it would still be с коллегой. Even though the word коллега can refer to a man or a woman, it ends in -а, so it always follows the feminine grammar rules for its endings.
Why is the verb напишет instead of пишет?
Пишет means "is writing" or "writes" (present tense). Adding the prefix на- makes it напишет, which is the perfective future tense. It means she "will write" the contract and complete it.
Договор (contract) is the direct object of the sentence. Why didn't its ending change?
As the direct object, договор is in the Accusative case. Because it is a masculine, inanimate (non-living) noun, its Accusative form looks exactly the same as its dictionary (Nominative) form.