Answer:
The first three translations:
1. Alice has to study for the exam. 'on behalf of' ?
3. Antonio leaves for work at six. 'specific time' or 'employment'.
Step-by-step explanation:
I didn't say the second translation because you already did that one :)
'por' means 'by'
'para' means 'for'.
So you could choose one of the 'enter answer(s)' to say why they used por or para. Its hard to explain but I hope this helps.