What is the daily limit for the number of coins won with social interactions?
If you answer a question, you can gain 15 coins up to five times a day, so you can get a total of 75 coins.
The same applies for commenting a friend's answer : you will obtain 15 coins up to five times a day, for a total of 75 coins.
Listening to a friend's answer will award you with 5 coins up to ten times a day, so you can obtain 50 coins this way.
In total, you can obtain 200 coins on a daily basis this way.